A hypothetical robot of microscopic proportions, built with nanotechnology. Such robots could assemble molecules one by one and are postulated to need self-replicating capabilities, as thousands of nanobots would be required to make anything on a size humans could use.

A nanotechnological robot nanomachine, also called a nanite, which is a mechanical or electromechanical device whose dimensions are measured in nanometers (millionths of a millimeter, or units of 10-9 meter. http://www.intel.com/education/makingchips/shock.htm

SF - A robot of microscopic proportions, presumably built by means of nanotechnology. As yet, only used informally (and speculatively!). Also called a nanoagent.