Slow, gig faltering in half-melted snow (8)
I believe the answer is:
sluggish
'slow' is the definition.
(I know that slow can be written as sluggish)
'gig faltering in half-melted snow' is the wordplay.
'faltering' is an anagram indicator.
'in' is an insertion indicator.
'half-melted snow' becomes 'slush' (I've seen this before).
'gig' is an anagram of 'ggi'.
'ggi' placed inside 'slush' is 'SLUGGISH'.
(Other definitions for sluggish that I've seen before include "Hardly speeding" , "Slow-moving like garden mollusc" , "Slow and apathetic" , "Lethargic" , "like a bullet?" .)