An entrance that may impress in the ring (5)

I believe the answer is:

agate

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'may impress in the ring' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'an entrance' is the wordplay.
'an' becomes 'a'.
'entrance' becomes 'gate' (type of entrance).
'a'+'gate'='AGATE'

'that' acts as a link.

Can you help me to learn more?

(Other definitions for agate that I've seen before include "marble" , "Semi-precious stone" , "Ornamental form of quartz" , "Precious stone" , "Variegated chalcedony" .)

I've seen this clue in The Globe and Mail.

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