Cheers a quiet student during interval (8)
I believe the answer is:
applause
'cheers' is the definition.
(thesaurus)
'a quiet student during interval' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'student' becomes 'l' (as in L-plates for learner drivers).
'during' indicates putting letters inside.
'interval' becomes 'pause' (pause is a kind of interval**).
'l' put into 'pause' is 'plause'.
'a'+'p'+'plause'='APPLAUSE'
(Other definitions for applause that I've seen before include "giving a hand?" , "Mark of appreciation like clapping and cheering" , "Approval shown by clapping" , "Gesture of approval" , "1a [BACALL] was in this musical" .)