A half pint's plenty for the captain! (5)
I believe the answer is:
pilot
'captain' is the definition.
(thesaurus)
'a half pint's plenty for the' is the wordplay.
'a half' means to take half the letters.
'plenty' becomes 'lo' (I can't explain this - if you can you should give a lot more credence to this answer).
'for' is a charade indicator (letters next to each other).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'pint' with half the letters taken is 'pi'.
'pi'+'lo'+'t'='PILOT'
Can you help me to learn more?
(Other definitions for pilot that I've seen before include "Plane's operator" , "Experimental scheme; flyer" , "Test or trial (project or programme)" , "Guide, leader" , "experimental programme" .)