Wide, albeit secondary highway (5)
I believe the answer is:
broad
'wide' is the definition.
(synonyms)
'albeit secondary highway' is the wordplay.
I cannot really see how this works, but
'highway' could be 'road' (highway is a type of road) and 'road' is located in the answer.
A single letter 'b' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for broad that I've seen before include "dame" , "not detailed" , "River expansion" , "Board (anag.)" , "Open" .)