Snatch unravelling garb (4)
I believe the answer is:
grab
'snatch' is the definition.
('grab' can be a synonym of 'snatch')
'unravelling garb' is the wordplay.
'unravelling' indicates anagramming the letters.
'garb' is an anagram of 'GRAB'.
(Other definitions for grab that I've seen before include "Seize suddenly" , "Brag about seizure" , "Take quickly" , "Seize roughly" , "Catch hold (of)" .)