Put on party attended by any number (3)
I believe the answer is:
don
'put on' is the definition.
(as in donning or putting on an item of clothing)
'party attended by any number' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'attended by' is a charade indicator (letters next to each other).
'any number' becomes 'n' (mathematical symbol for an unspecified number).
'do'+'n'='DON'
(Other definitions for don that I've seen before include "Spanish gent or Mafia chief" , "A mafia chief or Spanish grandee" , "Get into" , "Bradman, the ---" , "Spanish male title" .)