infinitesimal

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?”

   “"You will conceive a bunch of grapes," said he, "which are covered by some infinitesimal but noxious bacillus."”

   “Then you could say that the doorway exploded. But the particular verb doesn't do the action justice. Rather, it shattered into infinitesimal pieces.”

2. (not-comparable)Of or pertaining to non-zero quantities whose magnitude is less than any positive rational number.
3. (informal)Very small.

noun

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

   “It occurred to the hearer, who was accustomed to glean much of his knowledge from the infinitesimals of tone, that there was a spice of "It is my duty and I will" in this praiseworthy resolve which fell short of the ecstatic resolution of the Saturday Nora.”