A "roundabout" is an intersection (a) with either (i) one or more marked lanes, all of which are for the use of vehicles travelling in the same direction around a central traffic island; or(ii) room for one or more lines of traffic travelling in the same direction around a central traffic island; and(b) with or without a roundabout sign at each entrance.
Note 1
Intersection , marked lane , traffic and traffic island are defined in the dictionary.
Note 2
Rule 322(3) and (4) deal with the meaning of a traffic sign at a place.
Roundabout sign