Edge of a cup (3)
I believe the answer is:
lip
'edge of a cup' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lip that I've seen before include "Edge; impudent talk" , "Fleshy fold of mouth tissue" , "Rim of an orifice" , "giving such insincere service" , "Impudent talk from part of the face" .)