Spies supporting very large party (6)
I believe the answer is:
social
'party' is the definition.
(social is a kind of party)
'spies supporting very large' is the wordplay.
'spies' becomes 'cia'.
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'very' becomes 'so' (I've seen this in other clues).
'large' becomes 'l'.
'cia' put after 'so' is 'socia'.
'socia'+'l'='SOCIAL'
(Other definitions for social that I've seen before include "Official helping families with problems" , "Pertaining to human relations" , "Friendly - party" , "Relating to living together in communities" , "Of society or its organisation" .)