Wander onto the street, which is unusual (7)
I believe the answer is:
strange
'unusual' is the definition.
(similar in meaning)
'wander onto the street' is the wordplay.
'wander' becomes 'range' (synonyms).
'onto' says to put letters next to each other.
'the street' becomes 'st' (abbreviation).
'range' after 'st' is 'STRANGE'.
'which is' acts as a link.
(Other definitions for strange that I've seen before include "Unusual, surprising" , "Offbeat" , "Queer" , "Slightly odd, a bit weird" , "Weird, eerie" .)