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' means one lot of letters go next to another.
'the street' becomes 'st' (abbreviation).
'range' put 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" .)