Still one abominable snowman (4)
I believe the answer is:
yeti
'abominable snowman' is the definition.
(I've seen this in another clue)
'still one' is the wordplay.
'still' becomes 'yet' (yet can mean still or so far).
'one' becomes 'i' (Roman numeral).
'yet'+'i'='YETI'
(Other definitions for yeti that I've seen before include "Hairy recluse" , "Legendary Himalayan creature" , "supposed mountain creature" , "creature awaiting discovery?" , "highland inhabitant" .)