Crossword Genius

Notable work over a period (5)

Ross

I believe the answer is:

opera

I'm a little stuck... Click here to teach me more about this clue!

'notable' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'work over a period' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'a period' becomes 'era' (era is a kind of period).
'op'+'era'='OPERA'

Can you help me to learn more?

(Other definitions for opera that I've seen before include "Lulu, say" , "Dramatic genre" , "10 [NORMA], for example" , "Tosca, for example" , "Musical extravaganza" .)

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