Head of faculty coming in to pose riddle (4)
I believe the answer is:
sift
'riddle' is the definition.
(thesaurus)
'head of faculty coming in to pose' is the wordplay.
'head of' suggests taking the first letters.
'coming in to' indicates putting letters inside.
'pose' becomes 'sit' (sitting is a kind of posing).
The first letter of 'faculty' is 'f'.
'f' inserted within 'sit' is 'SIFT'.
(Other definitions for sift that I've seen before include "Get lumps from (flour)" , "Sieve, examine closely" , "Winnow out" , "Separate by passing through fine mesh" , "Sieve finely" .)