Is he keen to avoid duplicating a letter? (3)
I believe the answer is:
ken
'is he' is the definition.
'keen to avoid duplicating a letter?' is the wordplay.
I cannot really see how this works, but
'letter?' could be 'en' (I've seen this in other clues) and 'en' is found in the answer.
A single letter 'k' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ken that I've seen before include "Notice" , "Know; man's name" , "Awareness" , "Identify; -- Livingstone" , "Understanding - boy's name" .)