Crossword Genius

Score two less (8)

Ross

I believe the answer is:

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This might be a double definition.

'score' is the first definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe you can see an association between them that I can't see?

'two less' is the second definition.
The answer and definition can be both quantities as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

Can you help me to learn more?

(Other definitions for eighteen that I've seen before include "Number of holes on a golf course", "Number of on-field players in an Australian Rules football team", "age of maturity", "The genie (anag.)", "2x9".)