Was a thespian in charge of teaching (8)
I believe the answer is:
didactic
'of teaching' is the definition.
(didactic means relating to teaching)
'was a thespian in charge' is the wordplay.
'was a thespian' becomes 'did act' (thespian means an actor).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'didact'+'ic'='DIDACTIC'
(Other definitions for didactic that I've seen before include "Edifying" , "like a school-teacher?" , "Having the manner of one lecturing students" , "Imparting a lesson" , "Having a lecturing or moralising manner" .)