Term teacher initially wearing hat (5)
I believe the answer is:
title
'term' is the definition.
(thesaurus)
'teacher initially wearing hat' is the wordplay.
'initially' says to take the initial letters.
'wearing' means one lot of letters goes inside another.
'hat' becomes 'tile' (I've seen this before).
The first letter of 'teacher' is 't'.
't' inserted within 'tile' is 'TITLE'.
(Other definitions for title that I've seen before include "established claim to ownership" , "Sir, or madam" , "Right to possession" , "Legal possession" , "Caption; name" .)