He refused to accept tyranny or play the informer (4)
I believe the answer is:
tell
'he refused to accept tyranny or play' is the definition.
The definition suggests a singular noun but the answer is not.
'the informer' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'informer' becomes 'ell' (I can't justify this - if you can you should believe this answer much more).
't'+'ell'='TELL'
Can you help me to learn more?
(Other definitions for tell that I've seen before include "Make a difference" , "Instruct" , "Grass - Swiss hero" , "blow the whistle" , "Legendary Swiss crossbowman and folk hero" .)