Note short skirt (4)
I believe the answer is:
mini
'skirt' is the definition.
(a mini skirt)
'note short' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'short' becomes 'ni' (I can't justify this - if you can you should believe this answer much more).
'mi'+'ni'='MINI'
Can you help me to learn more?
(Other definitions for mini that I've seen before include "Cult British car" , "Car designed by Issigonis" , "Short skirt - small car" , "type of garment" , "(Car etc) of small size" .)