Crossword Genius

Bona, meliora, ____ : degrees of excellence in things (6)

Ross

I believe the answer is:

optima

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'things' is the definition.
The answer and definition can be both human attributes as well as being plural nouns.
Perhaps there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for optima that I've seen before include "Ideal conditions" , "Points at which conditions are most favourable" , "Conditions producing the best possible results" .)

I've seen this clue in The Times.
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