Martin is college head (4)
I believe the answer is:
dean
I believe this is a double definition.
'martin' is the first definition.
(Dean Martin)
'college head' is the second definition.
(I've seen this in another clue)
'is' acts as a link.
(Other definitions for dean that I've seen before include "Torvill's ice dancing partner" , "Small valley - cathedral dignitary" , "One is in charge of a university department" , "Cathedral chapter head" , "College official" .)