Any number in group becoming ecstatic (4)
I believe the answer is:
sent
'ecstatic' is the definition.
(send can mean to stimulate or excite)
'any number in group' is the wordplay.
'any number' becomes 'n' (mathematical symbol for an unspecified number).
'in' indicates putting letters inside.
'group' becomes 'set' (both can mean a collection).
'n' going inside 'set' is 'SENT'.
'becoming' acts as a link.
(Other definitions for sent that I've seen before include "Remitted" , "Told to go - enthralled" , "Caused to go somewhere" , "Thrilled" , "Posted" .)