Diana bewitched water nymph (5)
I believe the answer is:
naiad
'water nymph' is the definition.
(synonyms)
'diana bewitched' is the wordplay.
'bewitched' indicates anagramming the letters.
'diana' with letters rearranged gives 'NAIAD'.
(Other definitions for naiad that I've seen before include "Classic spirit" , "Aquatic larva of a dragonfly" , "Fabulous spring being" , "Greek mythological water nymph" , "watery spirit" .)