I become faint after lifting skirt (4)
I believe the answer is:
midi
'skirt' is the definition.
(I've seen this before)
'i become faint after lifting' is the wordplay.
'become faint' becomes 'dim'.
'after' says to put letters next to each other.
'lifting' shows that the letters should be reversed in order.
'i'+'dim'='idim'
'idim' in reverse letter order is 'MIDI'.
(Other definitions for midi that I've seen before include "Female attire" , "Cover reaching calves" , "Southern part of France" , "The south of France; a skirt length" , "Calf-length dress" .)