Old English county American feller soon takes in (5,5)
I believe the answer is:
anglo saxon
'old english' is the definition.
(synonyms)
'county american feller soon takes in' is the wordplay.
I cannot quite understand how this works, but
'county' could be 'glos' (abbreviation for Gloucestershire) and 'glos' is located in the answer.
'american' could be 'a' (common abbreviation - e.g. in organisation names) and 'a' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for anglo saxon that I've seen is " Earthy language".)