Leering nastily, taking in one's underwear (8)
I believe the answer is:
lingerie
'underwear' is the definition.
(type of underwear)
'leering nastily taking in one's' is the wordplay.
'nastily' indicates anagramming the letters.
'taking in' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'leering' is an anagram of 'lngerie'.
'lngerie' going around 'i' is 'LINGERIE'.
(Other definitions for lingerie that I've seen before include "flimsy stuff" , "One from W Atlantic island group" , "pants! Could be" , "Women's underwear and nightclothes" , "Garments" .)