Large cup (3)
I believe the answer is:
mug
'large cup' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mug that I've seen before include "Slangy victim, by gum" , "In slang, a person easily deceived" , "Drinking vessel; dupe" , "Fool - face - vessel" , "Beaker" .)