Item of clothing (7)
'item of clothing' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for garment that I've seen before include "Item of clothing" , "coat, say" , "Article of dress" , "Vestment" , "Perhaps shift" .)
(Other definitions for shirt that I've seen before include "Garment for upper male body, usually cotton" , "One may lose it at the bookie's" , "tailored garment" , "Man's garment" , "Male garment worn with tie" .)