Around one, check on really old Muscovite? (6)
I believe the answer is:
soviet
'old muscovite?' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?
'around one check on really' is the wordplay.
'around' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'check' becomes 'vet' (to vet someone is to check their background).
'on' says to put letters next to each other.
'really' becomes 'so' (both can mean 'extremely').
'i' going into 'vet' is 'viet'.
'viet' put after 'so' is 'SOVIET'.
Can you help me to learn more?
(Other definitions for soviet that I've seen before include "Elected council in a communist country" , "Cold war rival" , "Russian workers' council, originally" , "Old Russian council" , "Old government council" .)