Senior common room is most profligate first of all — economise (6)
I believe the answer is:
scrimp
'economise' is the definition.
(I've seen this before)
'senior common room is most profligate first of all' is the wordplay.
'first of all' says to take the initial letters.
The initial letters of 'senior common room is most profligate' is 'SCRIMP'.
(Other definitions for scrimp that I've seen before include "Treat stingily" , "Pinch and save" , "Practice economy" , "Beer maker" , "Make too small, stint" .)