Nymph of the woods evicting river couple (4)
I believe the answer is:
dyad
'couple' is the definition.
('dyad' can be a synonym of 'couple')
'nymph of the woods evicting river' is the wordplay.
'nymph of the woods' becomes 'dryad' (I've seen this before).
'evicting' indicates named letters should be taken away.
'river' becomes 'r'.
'dryad' with 'r' taken out is 'DYAD'.
(Other definitions for dyad that I've seen before include "Couple" , "Something in two parts" , "is in element" , "Pair" .)