Everyone seems to have the same set of letters. I used a quickie program to identify all the candidate substrings, then the program below to identify the words.

 

My sequence of letters is IART

 

iatr = diatribe

irat = admiration

irta = flirtation

itar = humanitarian

itra = arbitrage

airt = airtime

aitr = waitress

arit = angularity

arti = article

atir = satire

atri = patriarch

riat = appropriate

rita = authoritarian

rait = portrait

rati = ratio

rtia = impartial

rtai = certain

tiar = penitentiary

tira = multiracial

tair = stairs

tari = militarism

tria = equestrian

trai = constrain

The VB program is:

 

Imports System
Imports System.IO
Imports System.Text
Imports System.Runtime.InteropServices
Imports System.Math
Module Module1
    Sub Main()
        Randomize()
        Dim intsize1 As Integer
        Dim intloop1 As Integer
        Dim strwordlist(0) As String
        size_strwordlist(intsize1)
        ReDim strwordlist(intsize1)
        load_strwordlist(strwordlist, intloop1)
        While 100 > 0
            justdoit(strwordlist, intloop1)
        End While
    End Sub

    Sub justdoit(ByRef strwordlist, ByRef intloop1)
        Dim strsubstring(4) As String
        Dim strstring As String
        Dim strflag As String
loopgetstring:
        strstring = ""
        Console.WriteLine(" ")
        Console.WriteLine("Enter substring - or just hit enter for " & _
        "random string.")
        strstring = LCase(Console.ReadLine())
        If Len(strstring) <> 4 Then
            If strstring > " " Then
                GoTo loopgetstring
            End If
        End If
        If strstring <= " " Then
            random_substring(strsubstring)
        Else
            parse_substring(strstring, strsubstring)
            For index1 As Integer = 0 To 2
                For index2 As Integer = index1 + 1 To 3
                    If strsubstring(index1) = strsubstring(index2) Then
                        GoTo loopgetstring
                    End If
                Next
            Next
        End If
        Console.WriteLine(" ")
        strstring = ""
        For index1 As Integer = 0 To 3
            strstring &= strsubstring(index1)
        Next
        Console.WriteLine( _
        "substring = " & strstring)
        Console.WriteLine("Press ENTER to begin search")
        Console.ReadLine()
        Console.WriteLine(" ")
        check_strsubstring(strsubstring, strflag, _
        strwordlist, intloop1)
        If strflag = "n" Then
            Console.WriteLine(" ")
            Console.WriteLine("Not a good substring.")
        Else
            Exit Sub
        End If
    End Sub

    Sub random_substring(ByRef strsubstring)
        Dim intsubstring(4) As Integer
        For index1 As Integer = 0 To 3
randomloop:
            intsubstring(index1) = Int((26 - 1 + 1) * Rnd()) + 1
            If index1 > 0 Then
                For index2 As Integer = 0 To index1 - 1
                    If intsubstring(index1) = intsubstring(index2) Then
                        GoTo randomloop
                    End If
                Next
            End If
        Next
        For index1 As Integer = 0 To 3
            Select Case intsubstring(index1)
                Case 1
                    strsubstring(index1) = "a"
                Case 2
                    strsubstring(index1) = "b"
                Case 3
                    strsubstring(index1) = "c"
                Case 4
                    strsubstring(index1) = "d"
                Case 5
                    strsubstring(index1) = "e"
                Case 6
                    strsubstring(index1) = "f"
                Case 7
                    strsubstring(index1) = "g"
                Case 8
                    strsubstring(index1) = "h"
                Case 9
                    strsubstring(index1) = "i"
                Case 10
                    strsubstring(index1) = "j"
                Case 11
                    strsubstring(index1) = "k"
                Case 12
                    strsubstring(index1) = "l"
                Case 13
                    strsubstring(index1) = "m"
                Case 14
                    strsubstring(index1) = "n"
                Case 15
                    strsubstring(index1) = "o"
                Case 16
                    strsubstring(index1) = "p"
                Case 17
                    strsubstring(index1) = "q"
                Case 18
                    strsubstring(index1) = "r"
                Case 19
                    strsubstring(index1) = "s"
                Case 20
                    strsubstring(index1) = "t"
                Case 21
                    strsubstring(index1) = "u"
                Case 22
                    strsubstring(index1) = "v"
                Case 23
                    strsubstring(index1) = "w"
                Case 24
                    strsubstring(index1) = "x"
                Case 25
                    strsubstring(index1) = "y"
                Case 26
                    strsubstring(index1) = "z"
            End Select
        Next
    End Sub

    Sub parse_substring(ByRef strstring, ByRef strsubstring)
        For index1 As Integer = 1 To Len(strstring)
            strsubstring(index1 - 1) = Mid(strstring, index1, 1)
        Next
    End Sub

    Sub check_strsubstring(ByRef strsubstring, ByRef strflag, _
    ByRef strwordlist, ByRef intloop1)
        Dim strsearch As String
        Dim intcount As Integer
        Dim strnext As String
        strflag = "y"
        For index1 As Integer = 0 To 3
            For index2 As Integer = 0 To 3
                If index2 <> index1 Then
                    For index3 As Integer = 0 To 3
                        If index3 <> index1 And _
                        index3 <> index2 Then
                            For index4 As Integer = 0 To 3
                                If index4 <> index1 And _
                                index4 <> index2 And _
                                index4 <> index3 Then
                                    If Not ( _
                                    index1 = 0 And index2 = 1 And _
                                    index3 = 2 And index4 = 3) Then
                                        intcount = 0
                                        strsearch = "*" _
                                        & strsubstring(index1) _
                                        & strsubstring(index2) _
                                        & strsubstring(index3) _
                                        & strsubstring(index4) _
                                        & "*"
                                        display_words(strsearch, _
                                        strwordlist, intloop1, _
                                        intcount, _
                                        strnext)
                                        If intcount = 0 Then
                                            strflag = "n"
                                            Exit Sub
                                        End If
                                        If strnext = "s" Then
                                            Exit Sub
                                        End If
                                    End If
                                End If
                            Next
                        End If
                    Next
                End If
            Next
        Next
    End Sub

    Sub display_words(ByRef strsearch, _
    ByRef strwordlist, ByRef intloop1, _
    ByRef intcount, ByRef strnext)
        intcount = 0
        Console.WriteLine(" ")
        Console.WriteLine(strsearch)
        Console.ReadLine()
        For index1 As Integer = 0 To intloop1
            If strwordlist(index1) Like strsearch Then
                Console.WriteLine(strwordlist(index1))
                intcount += 1
                If (intcount Mod 20) = 0 Then
                    strnext = " "
                    Console.WriteLine("Next ? (p = permutation, s = substring)")
                    strnext = LCase(Console.ReadLine())
                    If strnext = "p" Or strnext = "s" Then
                        Exit Sub
                    End If
                End If
            End If
        Next
        If intcount = 0 Then
            Exit Sub
        End If
        strnext = " "
        Console.WriteLine("Next ? (p = permutation, s = substring)")
        strnext = LCase(Console.ReadLine())
        If strnext = "p" Or strnext = "s" Then
            Exit Sub
        End If
    End Sub

    Sub size_strwordlist(ByRef intsize1)
        Dim strstring As String
        Dim objStreamReader As StreamReader
        objStreamReader = _
        New StreamReader("C:\VB.WORD.MASTER")
        intsize1 = 0
        While 100 > 0
            strstring = LCase(objStreamReader.ReadLine)
            If strstring <= " " Then
                Exit While
            End If
            intsize1 += 1
        End While
        objStreamReader.Close()
    End Sub

    Sub load_strwordlist(ByRef strwordlist, ByRef intloop1)
        Dim strstring As String
        Dim objStreamReader As StreamReader
        objStreamReader = _
        New StreamReader("C:\VB.WORD.MASTER")
        intloop1 = -1
        While 100 > 0
            strstring = LCase(objStreamReader.ReadLine)
            If strstring <= " " Then
                Exit While
            End If
            intloop1 += 1
            strwordlist(intloop1) = strstring
        End While
        objStreamReader.Close()
    End Sub
End Module