What he does is appropriate (5)
I believe the answer is:
thief
'what he does is appropriate' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'what he' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'hi' and 'hi' is found within the answer.
The remaining letters 'tef' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for thief that I've seen before include "Crook" , "Aus. or Scots city" , "A robber or pickpocket" , "Raffles, say" , "One who steals" .)