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 am 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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