Pertaining to the mouth (4)
I believe the answer is:
oral
'pertaining to the mouth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oral that I've seen before include "By word of mouth, say exam" , "Exam using speech" , "Verbal" , "'Spoken, not written (4)'" , "Kind of exam" .)