Skirt wrapped in canopy for a period of three months (9)
I believe the answer is:
trimester
'a period of three months' is the definition.
(I've seen this before)
'skirt wrapped in canopy' is the wordplay.
'skirt' becomes 'rim' (both can mean something's edge).
'wrapped in' is an insertion indicator.
'canopy' becomes 'tester' (I've seen this in another clue).
'rim' placed into 'tester' is 'TRIMESTER'.
'for' acts as a link.
(Other definitions for trimester that I've seen before include "US academic term" , "academic session" , "Period of three months" , "American term" , "part of college year" .)