Relative on a road, initially, that's foggy (7)
I believe the answer is:
unclear
'that's foggy' is the definition.
(thesaurus)
'relative on a road initially' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'initially' indicates taking the first letters.
The first letter of 'road' is 'r'.
'uncle'+'a'+'r'='UNCLEAR'
(Other definitions for unclear that I've seen before include "Not easy to see or understand" , "Ambiguous" , "Not transparent or intelligible" , "in clouds?" , "Not apparent" .)