Submit shortly after sex (5)
I believe the answer is:
posit
'submit' is the definition.
(thesaurus)
'shortly after sex' is the wordplay.
'shortly' means to remove the last letter.
'after' becomes 'post' (I've seen this before).
'sex' becomes 'it' (a common euphemism).
'post' with its last letter taken away is 'pos'.
'pos'+'it'='POSIT'
(Other definitions for posit that I've seen before include "Put forward (a theory)" , "Put forward (something) as a given" , "Put forward (an idea)" , "Assume as fact for argument's sake" , "Assume as fact, postulate" .)