Intrepid bachelor leaving for party (4)
I believe the answer is:
rave
'for party' is the definition.
(type of dance party)
'intrepid bachelor leaving' is the wordplay.
'intrepid' becomes 'brave' (synonyms).
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'leaving' indicates named letters should be taken away.
'brave' with 'b' taken out is 'RAVE'.
(Other definitions for rave that I've seen before include "modern dance music" , "Laudatory sort of review - quite a rant" , "Enthuse; rant" , "Talk wildly and irrationally" , "Party with electronic dance music - be wild" .)