infinitesimal

Etymology

From Latin infinitesimus, from infinitus (“infinite”) + -esimus, as in centesimus (“hundredth”).

adj

1. Incalculably, exceedingly, or immeasurably minute; vanishingly small.
   Do you ever get the feeling that you are but an infinitesimal speck, swallowed by the vastness of the universe and beyond?
   Then you could say that the doorway exploded. But the particular verb doesn't do the action justice. Rather, it shattered into infinitesimal pieces. 2001, Eoin Colfer, Artemis Fowl, page 221
2. (mathematics) Of or pertaining to values that approach zero as a limit.
3. (informal) Very small.

noun

1. (mathematics) A non-zero quantity whose magnitude is smaller than any positive number (by definition it is not a real number).