Note short skirt on model initially (5)
I believe the answer is:
minim
'note' is the definition.
(type of musical note)
'short skirt on model initially' is the wordplay.
'short skirt' becomes 'mini' (mini skirt).
'on' means one lot of letters go next to another.
'initially' says to take the initial letters.
The initial letter of 'model' is 'm'.
'mini'+'m'='MINIM'
(Other definitions for minim that I've seen before include "Note equal to two crochets" , "Feature of a score" , "Two crotchets in one" , "Note of two crotchets" , "Double crotchet" .)