River forms meandering line (4)
I believe the answer is:
nile
'river' is the definition.
(I know that Nile is a river)
'meandering line' is the wordplay.
'meandering' indicates anagramming the letters.
'line' anagrammed gives 'NILE'.
'forms' is the link.
(Other definitions for nile that I've seen before include "River (which is originally blue and white)" , "Cairo's river" , "Line (anag)" , "eastern flower" , "River of eastern Africa" .)