Water nymph (5)
I believe the answer is:
naiad
'water nymph' is the definition.
(naiad is a kind of water nymph)
This is the entire clue.
(Other definitions for naiad that I've seen before include "Mythological water-nymph" , "divine female figure" , "Spring nymph" , "Nymph of lakes, springs and rivers" , "Fabulous spring being" .)