Small whip cut (5)
I believe the answer is:
slash
'cut' is the definition.
(slash is a kind of cut)
'small whip' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'whip' becomes 'lash' ('lash' can be a synonym of 'whip').
's'+'lash'='SLASH'
(Other definitions for slash that I've seen before include "Punctuation mark" , "Cut crudely" , "Cut as with a sword - /" , "Wee stroke < /" , "Violently cut" .)