Stick in part of mouth (3)
I believe the answer is:
gum
This clue is a triple definition!
'stick' is the first definition.
(thesaurus)
'in' acts as a link.
'part' is the second definition.
(gum is a kind of part)
'of' acts as a link.
'mouth' is the third definition.
(thesaurus)
(Other definitions for gum that I've seen before include "Adhesive for chewing" , "Chewy stuff, hard to clean away" , "To stick with adhesive" , "Prepartion for sticking or chewing" , "Chewed sweet" .)