A cyclone is a huge and powerful storm. A cyclone consists of a low pressure area with high pressure all around. High speed winds go around the centre violently and are accompanied by heavy rains.They have large diameters.
A tornado is violent, twisted funnel of high speed wind. It is formed when a funnel like column of cold air sinks down from a story cloud. Warm air rises up which whirls up causing high speed circulating winds.They have relatively smaller diameter.