Temporary pact in Greek cases (6)
I believe the answer is:
acting
'temporary' is the definition.
(similar in meaning)
'pact in greek cases' is the wordplay.
'cases' says the answer is hidden in the clue.
'ACTING' is hidden in the letters of 'pact in greek'.
(Other definitions for acting that I've seen before include "Temporary - work in the theatre" , "Stand-in" , "Taking a part - on a temporary basis" , "Playing like thespian" , "Behaving like a player" .)