Envoy's degree document, first from Trinity (8)
I believe the answer is:
diplomat
'envoy's' is the definition.
(I've seen this before)
'degree document first from trinity' is the wordplay.
'degree document' becomes 'diploma' (I've seen this before).
'first from trinity' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'diploma'+'t'='DIPLOMAT'
Can you help me to learn more?
(Other definitions for diplomat that I've seen before include "tactful one" , "An ambassador or tactful person" , "One who represents his govermnent abroad" , "Tactful person, maybe in public service" , "Our Man in Havana" .)