A mere agent may make one (9)

I believe the answer is:

agreement

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'one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'a mere agent may make' is the wordplay.
'may make' is an anagram indicator (I've seen this in other clues).
'mere'+'agent'='mereagent'
'mereagent' anagrammed gives 'AGREEMENT'.

Can you help me to learn more?

(Other definitions for agreement that I've seen before include "Harmony, concurrence" , "Pact" , "Unlikely result" , "Harmony of opinion" , "consensus" .)

I've seen this clue in The Irish News.

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