River nymph (5)
I believe the answer is:
naiad
'river nymph' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for naiad that I've seen before include "divine female figure" , "Spring nymph" , "Greek mythological water nymph" , "Nymph of lakes, springs and rivers" , "River nymph" .)