Thoroughfare is wide, with one side closed off (4)
I believe the answer is:
road
'thoroughfare' is the definition.
(a thoroughfare is a type of road)
'wide with one side closed off' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'a' and 'a' is found in the answer.
'side' could be 'r' (abbreviation for right) and 'r' is located in the answer.
The remaining letters 'od' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for road that I've seen before include "Parting guests used to take 'one for the --'" , "Path" , "Way to achieving a particular outcome" , "Way from A to B" , "'The . . . . to hell is paved with good intentions'" .)