Garment made of piece of cloth that's mostly light (6)
I believe the answer is:
raglan
'garment' is the definition.
(raglan is a kind of garment)
'piece of cloth that's mostly light' is the wordplay.
'piece of cloth' becomes 'rag' (rag is a kind of piece of cloth).
'that's mostly' means to remove the last letter.
'light' becomes 'land' (I've seen this before).
'land' with its last letter taken off is 'lan'.
'rag'+'lan'='RAGLAN'
'made of' is the link.
(Other definitions for raglan that I've seen before include "Type of 12" , "Style of sleeve" , "Garment defined by its sleeves" , "Type of sleeve or overcoat" , "Kind of sleeve that continues to the neck" .)