Terribly hot, no good for skimpy underwear (5)
I believe the answer is:
thong
'skimpy underwear' is the definition.
(a thong is a skimpy type of underwear)
'terribly hot no good' is the wordplay.
'terribly' indicates anagramming the letters.
'no good' becomes 'ng' (abbreviation).
'hot' is an anagram of 'tho'.
'tho'+'ng'='THONG'
'for' acts as a link.
(Other definitions for thong that I've seen before include "Insubstantial underwear" , "Thin leather strip" , "Lash of whip" , "Frequently (archaic)" , "article of clothing" .)