Knight crossing main road by city is fairly close (7)
I believe the answer is:
similar
'fairly close' is the definition.
'knight crossing main road by city' is the wordplay.
'knight' becomes 'sir' (I've seen this before).
'crossing' indicates putting letters inside.
'main road' becomes 'mi'.
'by' means one lot of letters go next to another.
'city' becomes 'la' (Los Angeles).
'mi'+'la'='mila'
'sir' placed around 'mila' is 'SIMILAR'.
'is' acts as a link.
(Other definitions for similar that I've seen before include "Of the same kind" , "Alike, resembling" , "Appearing the same" , "Resembling, like" , "Comparable" .)