A rotating funnel-shaped cloud that does not touch the ground is called a funnel cloud.
A funnel cloud is made visible when water vapor condenses into droplets inside a rotating column of air extending downward from a cloud base, usually a cumulonimbus or towering cumulus cloud. The visible funnel is not the entire vortex: much of the rotating air may be invisible, and condensation depends on temperature and moisture.
Funnel clouds occur most often with supercell thunderstorms and can be an early visual sign of tornadic development. If the circulation reaches the surface, meteorologists classify the phenomenon as a tornado, even if a complete visible funnel is absent. A tornado can sometimes be identified by rotating debris or other surface effects before a condensation funnel appears.
A waterspout is not the same answer here: it is a tornado occurring over water, though some fair-weather waterspouts form by a different process. Dust devils are also rotating columns, but they are generally surface-based and not descended from a thunderstorm cloud.