Fruity thing like that wearing knickers (6)
I believe the answer is:
damson
'fruity thing' is the definition.
(damson is a kind of fruit)
'like that wearing knickers' is the wordplay.
'like that' becomes 'so' (as in 'like so').
'wearing' means one lot of letters goes inside another.
'knickers' becomes 'damn' (as an interjection).
'so' placed inside 'damn' is 'DAMSON'.
(Other definitions for damson that I've seen before include "Sort of plum" , "Small fruit for nomads" , "fruit tree" , "Small plum-like fruit" , "Wild plum" .)