Diana as a mythical nymph (5)

I believe the answer is:

naiad

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'nymph' is the definition.
(naiad is a kind of nymph)

'diana as a mythical' is the wordplay.
'diana' anagrams to 'NAIAD'.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for naiad that I've seen before include "Mythological water-nymph" , "Nymph of lakes, springs and rivers" , "Greek mythological water nymph" , "Diana (anag.)" , "Fabulous spring being" .)

I've seen this clue in the Evening Standard.

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