Plant is no distance from river (8)
I believe the answer is:
camomile
'river' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'plant is no distance' is the wordplay.
'plant' becomes 'cam' (I can't justify this - if you can you should believe this answer much more).
'is no' becomes 'o' (resembles 0 - 'no' can mean 'zero').
'distance' becomes 'mile'.
'cam'+'o'+'mile'='CAMOMILE'
'from' is the link.
(Other definitions for camomile that I've seen before include "Wild flower used medicinally and for tea" , "Sweet-smelling plant used to make medicine and lotion" , "Herb for tea (or lawn?)" , "Aromatic plant, flavouring tea" , "Plant used for making herbal drink" .)