Costume is hot, somewhat (5)
I believe the answer is:
habit
'costume' is the definition.
(thesaurus)
'hot somewhat' is the wordplay.
'hot' becomes 'h'.
'somewhat' becomes 'abit' (a bit).
'h'+'abit'='HABIT'
'is' is the link.
(Other definitions for habit that I've seen before include "Monk's gown or custom" , "Acquired pattern of behaviour" , "Usual practice; garment" , "Custom, nun's wear" , "What might one have a regular tendency to" .)