Academic briefly in favour of opening of faculty (4)
I believe the answer is:
prof
'academic briefly' is the definition.
(I've seen this before)
'in favour of opening of faculty' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'opening of' suggests taking the first letters.
The initial letter of 'faculty' is 'f'.
'pro'+'f'='PROF'
(Other definitions for prof that I've seen before include "Senior academic (colloq.)" , "One holding chair" , "head of dept at uni" , "Top academic (informal)" , "teacher" .)