Lip — part of the face (5)
I believe the answer is:
cheek
This clue is a triple definition!
'lip' is the first definition.
(I've seen this before)
'part' is the second definition.
(cheek is a kind of part)
'of' acts as a link.
'the face' is the third definition.
('cheek' can be a synonym of 'face')
(Other definitions for cheek that I've seen before include "on one's face?" , "Disrespectful talk" , "Informal impertinence from side of face" , "Effrontery" , "Part of face or informal impudence" .)