Try and stop E and smack when out of head (9)
I believe the answer is:
endeavour
'try' is the definition.
(I know that try can be written as endeavour)
'stop e and smack when out of head' is the wordplay.
'stop e' becomes 'ende' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'smack' becomes 'savour' (synonyms).
'when out of head' means to remove the first letter.
'savour' with its initial letter taken off is 'avour'.
'ende'+'avour'='ENDEAVOUR'
'and' is the link.
Can you help me to learn more?
(Other definitions for endeavour that I've seen before include "Try - Cook's ship" , "Attempt by employing effort" , "Determined attempt" , "Make a serious effort" , "Undertaking" .)