Sharp answer in Tripos test (7)
I believe the answer is:
riposte
'sharp answer' is the definition.
(I've seen this before)
'in tripos test' is the wordplay.
'in' indicates a hidden word.
'RIPOSTE' is hidden within 'tripos test'.
(Other definitions for riposte that I've seen before include "Repartee; quick thrust (fencing)" , "Poster I alter for repartee" , "Snappy comeback" , "Rejoin" , "Witty comeback" .)