Polite invalid accepting kiss for heroic deed (7)
I believe the answer is:
exploit
'heroic deed' is the definition.
(I've seen this before)
'polite invalid accepting kiss' is the wordplay.
'invalid' indicates an anagram (invalid or wrong spelling).
'accepting' indicates putting letters inside (inserted letters are accepted).
'kiss' becomes 'x' (X can represent a kiss).
'polite' is an anagram of 'eploit'.
'eploit' placed around 'x' is 'EXPLOIT'.
'for' acts as a link.
(Other definitions for exploit that I've seen before include "Make good or selfish use of" , "put to good use" , "Daring feat; use unfairly" , "Use to advantage" , "Fleece?" .)