States previously ... "Cancel ring-shaped part!" (7)
I believe the answer is:
annulus
'ring-shaped part' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'states previously cancel' is the wordplay.
'states' becomes 'US' (abbreviation for the United States).
'previously' means one lot of letters go next to another.
'cancel' becomes 'annul' (annulling is a kind of cancelling).
'us' put after 'annul' is 'ANNULUS'.
Can you help me to learn more?
(Other definitions for annulus that I've seen before include "Ring-shaped object" , "Ring-shaped structure" .)