Calf-length dress (4)
I believe the answer is:
midi
'calf-length dress' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for midi that I've seen before include "Calf-length dress" , "Calf-length skirt" , "Le ..., the south of France" , "Half-length coat" , "The south of France; a skirt length" .)