Odd mountains behind street (7)
I believe the answer is:
strange
'odd' is the definition.
(I've seen this before)
'mountains behind street' is the wordplay.
'mountains' becomes 'range' (I've seen this before).
'behind' says to put letters next to each other.
'street' becomes 'st'.
'range' put after 'st' is 'STRANGE'.
(Other definitions for strange that I've seen before include "Odd, peculiar" , "Abnormal" , "Funny" , "Different" , "Queer" .)