English college servant has to enter unknown antiquary’s study (10)
I believe the answer is:
egyptology
'antiquary's study' is the definition.
(study of ancient Egypt)
'english college servant has to enter unknown' is the wordplay.
'english' becomes 'E' (abbreviation).
'college servant' becomes 'gyp' (I've seen this before).
'has' is a charade indicator (letters next to each other).
'enter unknown' becomes 'logy' (I can't justify this - if you can you should give a lot more credence to this answer).
'e'+'gyp'+'to'+'logy'='EGYPTOLOGY'
(Other definitions for egyptology that I've seen before include "digging into sand?" , "Pharaonic studies" , "Study of Pharaonic times" , "Study of pharaohs, etc" , "ancient field" .)