Platform, retro, empty on street — strange (7)
I believe the answer is:
rostrum
'platform' is the definition.
(I know that rostrum is a type of platform)
'retro empty on street strange' is the wordplay.
'empty' suggests removing the centre.
'on' says to put letters next to each other.
'street' becomes 'st' (abbreviation).
'strange' becomes 'rum' (similar in meaning).
'retro' with its centre taken out is 'ro'.
'ro'+'st'+'rum'='ROSTRUM'
(Other definitions for rostrum that I've seen before include "Platform for orchestra conductor" , "At which one may conduct" , "Platform for public speaking" , "beak" , "Podium" .)