Possibly “long” garment (6)
I believe the answer is:
jumper
'garment' is the definition.
(jumper is a kind of garment)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for jumper that I've seen before include "Pullover; circuit wire" , "Kangaroo and knitted garment" , "Horse, athlete and knitted garment" , "Woolly" , "field athlete" .)