Garment unsuitable for someone already hot (7)
I believe the answer is:
sweater
'garment' is the definition.
(sweater is a kind of garment)
'unsuitable for someone already hot' is the wordplay.
I cannot quite understand how this works, but
'someone' could be 'eater' (eater is a kind of someone) and 'eater' is present in the answer.
This explanation may well be incorrect...
(Other definitions for sweater that I've seen before include "Warm garment" , "One visibly too hot" , "Re waste: it's a garment" , "Top" , "Jumper (7)" .)