Leering horribly, clutching one's underwear (8)
I believe the answer is:
lingerie
'underwear' is the definition.
(lingerie is a kind of underwear)
'leering horribly clutching one's' is the wordplay.
'horribly' indicates anagramming the letters.
'clutching' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'leering' is an anagram of 'lingere'.
'lingere' going around 'i' is 'LINGERIE'.
(Other definitions for lingerie that I've seen before include "One from W Atlantic island group" , "Scanties" , "Women's underwear and nightclothes" , "Slinky undergarments" , "Women's underwear from France" .)