Each of the words an, am, at, come, rate and many others can be transformed into a new valid word by adding a prefix be.
The following list consists of 16 words, which may be sorted into 4 groups, each of 4 words fitting the same two-letter prefix, specific for that group.
One such group needs KN as a prefix.
Other 2-letter prefixes are up to you to find.
All 16 words must be used.

1. able
2. aid
3. air
4. and
5. ant
6. art
7. ash
8. ave
9. easy
10. eel
11. idle
12. irk
13. other
14. out
15. own
16. ows

(In reply to re: with computer assistance by Ady TZIDON)

I see that one can replace STOUT with STOWS, enabling using KNOUT instead of KNOWS.  However, KNOUT is not in my working vocabulary. In fact, it is being flagged as a spelling error as I type this.

Posted by Charlie on 2016-08-16 19:25:11