Definition of "infinitesimal" in English

adjective

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?

2. (mathematics, not comparable) Of or pertaining to non-zero quantities whose magnitude is less than any positive rational number.

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).