Garment with a band size (3)
I believe the answer is:
bra
'garment with a band size' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bra that I've seen before include "Female undergarment" , "Underwear item" , "one carrying chest" , "I give a couple a lift" , "support" .)