There is a certain common word in English language (say XYZ) such that prefixing it with a letter A creates a new word (AXYZ) that is a plural of another valid English word.

Find it - preferably with pen, paper and your knowledge only.

There is a possibility for several answers...

(In reply to re: Eureka! by Ady TZIDON)

Nothing in the problem requires XYZ to be a noun.  Ady, please correct your criticism of Jer's very valid answer, AHAS.  

Posted by Steve Herman on 2017-08-01 10:10:39