Crossword Genius

Maybe many decades are viewed in retrospect (3)

Ross

I believe the answer is:

era

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

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

'maybe many decades are viewed' is the wordplay.
'are' anagrams to 'ERA'.
But, I am not sure how the anagram is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for era that I've seen before include "Epoch, period" , "Geological period" , "Are involved in time span" , "Distinctive period of time" , "Geological age" .)

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