Definition of "infinitesimal"

infinitesimal

/ˌɪnfɪnɪˈtɛsɪməl/

adjective
comparative more infinitesimal, superlative most infinitesimal
1. Incalculably, exceedingly, or immeasurably minute; vanishingly small.
  Quotations
  "You will conceive a bunch of grapes," said he, "which are covered by some infinitesimal but noxious bacillus."
  1913, Arthur Conan Doyle, “(please specify the page)”, in The Poison Belt […], London; New York, N.Y.: Hodder and Stoughton
  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
plural infinitesimals
1. (mathematics) A non-zero quantity whose magnitude is smaller than any positive number (by definition it is not a real number).