Days of iridescence? (4)

I believe the answer is:

ides

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'days of iridescence?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'of iridescence?' is the wordplay.
'of' indicates a hidden word.
'IDES' is hidden in the letters of 'iridescence'.

Can you help me to learn more?

(Other definitions for ides that I've seen before include "Fatal March date or Julius Caesar" , "Julius Caesar died in these March days" , "March day Caesar died" , "Caesar was killed in this side of March" , "Caesar's fateful day" .)

I've seen this clue in the Evening Standard.

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