Join English diplomat (7)
I believe the answer is:
attache
'diplomat' is the definition.
(I know that attache is a type of diplomat)
'join english' is the wordplay.
'join' becomes 'attach' (attaching is a kind of joining).
'english' becomes 'e' (abbreviation).
'attach'+'e'='ATTACHE'
(Other definitions for attache that I've seen before include "Specialised envoy" , "Specialist on embassy staff" , "One on embassy staff" , "Man with a mission" , "Specialist diplomat" .)