Aromatic bulb (6)
'aromatic bulb' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for garlic that I've seen before include "Pungent member of onion family" , "Pungent plant" , "Kitchen additive" , "Bulb used in cooking" , "Flavouring plant" .)
(Other definitions for onion that I've seen before include "Head (slang); vegetable" , "Edible tear-jerker" , "Bulb used in cooking" , "The tear-inducing vegetable" , "Pungent vegetable" .)