Belong or conform (5)
I believe this is a double definition.
'belong' is the first definition.
(I've seen this in another clue)
'conform' is the second definition.
(I've seen this before)
(Other definitions for fit in that I've seen before include "Conform after adjustment" , "Belong" , "Be in harmony (with)" , "Find time for" , "Not be out of place" .)