Extremely small: nanoid.
One-billionth (10-9): nanometer.
A prefix meaning one billionth.
nano/nan'oh/ n. [CMU: from `nanosecond'] A brief period of time. "Be with you in a nano" means you really will be free shortly, i.e., implies what mainstream people mean by "in a jiffy" (whereas the hackish use of `jiffy' is quite different -- see jiffy).
North American Neuro-Ophthalmology Society