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