Cut with small whip (5)
I believe the answer is:
slash
'cut' is the definition.
(I know that slash is a type of cut)
'with small whip' is the wordplay.
'with' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'whip' becomes 'lash' (synonyms).
's' next to 'lash' is 'SLASH'.
(Other definitions for slash that I've seen before include "something between a month and a year" , "rent" , "Oblique stroke" , "Cut with sweeping strokes" , "Punctuation mark" .)