Drop off short skirt to be collected by stunner (8)
I believe the answer is:
diminish
'drop off' is the definition.
(thesaurus)
'short skirt to be collected by stunner' is the wordplay.
'short skirt' becomes 'mini' (I've seen this before).
'to be collected by' indicates putting letters inside.
'stunner' becomes 'dish' (informal term for an attractive person).
'mini' placed within 'dish' is 'DIMINISH'.
(Other definitions for diminish that I've seen before include "sink" , "Make less with mini dish" , "make shorter" , "Grow smaller, shrink" , "Make reduction" .)