Multitude in hurry, very cramped (4)
I believe the answer is:
hive
'multitude' is the definition.
(thesaurus)
'hurry very cramped' is the wordplay.
'hurry' becomes 'hie' ('hie' can be a synonym of 'hurry').
'very' becomes 'v' (abbreviation).
'cramped' indicates putting letters inside.
'hie' placed around 'v' is 'HIVE'.
'in' is the link.
(Other definitions for hive that I've seen before include "Scene of activity" , "A box for bees" , "busy scene" , "home of queen" , "Place swarming with activity" .)