Senior teacher (4)
'senior teacher' is the definition.
(short for head teacher)
This is the entire clue.
(Other definitions for head that I've seen before include "Chief; bonce" , "Edible part of cabbage" , "Cranium" , "School boss" , "Skull" .)
'senior teacher' is the definition.
(teacher in charge of a school)
This is all the clue.
(Other definitions for headmaster that I've seen before include "School manager" , "Top (male) teacher" , "Principal" .)