An Etymological Dictionary of Astronomy and Astrophysics

General: Indefinitely or exceedingly small.
Math.: A variable that approaches zero as a limit. A quantity decreasing indefinitely without actually becoming zero.

Etymology (EN): Infinitesimal, coined by Ger. philosopher and mathematician Baron Gottfried Wilhelm von Leibniz (1646-1716) from N.L. infinitesim(us) “infinite in rank,” from infinit(us), → infinite, + -esimus suffix of ordinal numerals + → -al.

Etymology (PE): Bikarânxord, from bikarân “unbounded, unlimited, infinite,”
from bi- “without” + karân “boundary, side, end” (variants karâné, kenâr, from Mid.Pers. karân, karânak, kenâr “edge, limit, boundary,” Av. karana- “side, boundary, end”)

• xord “minute, little, small” (from Mid.Pers. xvart, xôrt “small, insignificant;” Av. ādra- “weak, dependent;” Skt. ādhrá- “small, weak, poor,” nādh “to be oppressed;” Gk. nothros “sluggish;” PIE base *nhdhro-).