People supporting party gift (8)
I believe the answer is:
donation
'gift' is the definition.
(I know that donation is a type of gift)
'people supporting party' is the wordplay.
'people' becomes 'nation'.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'party' becomes 'do' (do can informally mean a party).
'nation' after 'do' is 'DONATION'.
(Other definitions for donation that I've seen before include "Money given to charity" , "present" , "Gift or contribution" , "An offering or charitable gift" , "Do anoint by way of a gift" .)