Term teacher's head wearing hat (5)
I believe the answer is:
title
'term' is the definition.
(thesaurus)
'teacher's head wearing hat' is the wordplay.
'head' says to take the initial letters.
'wearing' indicates putting letters inside.
'hat' becomes 'tile' (old-fashioned term for a hat).
The first letter of 'teachers' is 't'.
't' placed inside 'tile' is 'TITLE'.
(Other definitions for title that I've seen before include "Name; heading" , "Name of, eg, book" , "Handle" , "Right - name - address" , "Chapter heading" .)