Ring Houses of Parliament initially about nothing (4)
I believe the answer is:
hoop
'ring' is the definition.
(synonyms)
'houses of parliament initially about nothing' is the wordplay.
'initially' suggests taking the first letters.
'about' indicates putting letters inside.
'nothing' becomes 'o' (looks like zero - 0).
The first letters of 'houses of parliament' is 'hop'.
'hop' placed around 'o' is 'HOOP'.
(Other definitions for hoop that I've seen before include "Circular band; child's toy" , "Ring of wood - arch at croquet" , "Wood, metal or plastic band" , "Arch used in croquet" , "Large ring" .)