Be uncomfortably hot (7)
I believe the answer is:
swelter
'be uncomfortably hot' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for swelter that I've seen before include "Endure oppressive heat" , "Endure great heat" , "Be too hot; Gormenghast chef" , "Be uncomfortably hot as in the sun" , "Suffer oppressive heat" .)