Notable work over a period (5)
I believe the answer is:
opera
'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" .)