Bachelor with no date gatecrashing weirdly arcane shindig (4,5)
I believe the answer is:
barn dance
'shindig' is the definition.
(thesaurus)
'bachelor with no date gatecrashing weirdly arcane' is the wordplay.
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'with' is a charade indicator (letters next to each other).
'no date' becomes 'nd'.
'gatecrashing' means one lot of letters goes inside another.
'weirdly' indicates an anagram.
'arcane' is an anagram of 'arance'.
'nd' inserted into 'arance' is 'arndance'.
'b'+'arndance'='BARN DANCE'
(Other definitions for barn dance that I've seen before include "Rural entertainment" , "disco at the farm" , "Country social gathering" , "Kind of social event with traditional music" , "Country entertainment" .)