Each is English, extremely (5)
I believe the answer is:
every
'each' is the definition.
(synonyms)
'english extremely' is the wordplay.
'english' becomes 'e' (abbreviation).
'extremely' becomes 'very' (very can mean extremely or considerably).
'e'+'very'='EVERY'
'is' is the link.
(Other definitions for every that I've seen before include "The best possible" , "'God bless us - - one !'" , "Each one without exception" , "Each (one of a set)" , "Each of a number" .)