Cheek is a part of the face (3)
I believe the answer is:
lip
I believe this is a double definition.
'cheek' is the first definition.
(both can mean insolence or rudeness)
'a part of the face' is the second definition.
('lip' is part of 'face')
'is' is the link.
(Other definitions for lip that I've seen before include "Sauce" , "Impudent talk from part of the face" , "Rim; impertinence" , "It can be read" , "Part of mouth or cheek" .)