Informal garment (1-5)
I believe the answer is:
t-shirt
'informal garment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for t-shirt that I've seen before include "Simple garment" , "Informal collarless top" , "Close-fitting pullover shirt" , "Collarless pullover shirt" , "Pullover top" .)