Item of clothing
'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" .)