Relative by a river, hazy (7)
I believe the answer is:
unclear
'hazy' is the definition.
(I know that hazy can be written as unclear)
'relative by a river' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'by' says to put letters next to each other.
'river' becomes 'r' (abbreviation for river).
'uncle'+'a'+'r'='UNCLEAR'
(Other definitions for unclear that I've seen before include "Ill-defined or not easily understood" , "Poorly described" , "Not certain" , "Not easy to grasp" , "in clouds?" .)