Large cup without a saucer (3)
I believe the answer is:
mug
'large cup without a saucer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mug that I've seen before include "A drinking vesel or a slangy victim" , "concentrate on studying" , "Beaker" , "Drinking vessel; rob" , "One easily duped" .)