Examiner buttons lip for a term (9)
I believe the answer is:
trimester
'term' is the definition.
(I know that trimester is a type of academic session)
'examiner buttons lip' is the wordplay.
'examiner' becomes 'tester' (synonyms).
'buttons' means one lot of letters goes inside another (button can mean to fasten or contain using buttons).
'lip' becomes 'rim' (synonyms).
'tester' placed around 'rim' is 'TRIMESTER'.
'for a' is the link.
(Other definitions for trimester that I've seen before include "part of college year" , "American term" , "academic session" , "Period of three months" , "US academic term" .)