An Etymological Dictionary of Astronomy and Astrophysics

Quick, at once or without delay.

Etymology (EN): M.E., from O.Fr. prompt, from L. promptus “brought forth, ready, quick,” p.p. of promere “to bring forth,” from → pro- “forward” + emere “to take.”

Etymology (PE): Tond, “swift, rapid, brisk; fierce, severe,” Mid.Pers. tund “sharp, violent;” Sogdian tund “violent;” cf. Skt. tod- “to thrust, give a push,” tudáti “he thrusts;” L. tundere “to thrust, to hit” (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere “to thrust or bore through,” from per- + tundere, as explained); PIE base *(s)teud- “to thrust, to beat.”
Biderang “without delay,” from bi- negation prefix, → in-, + derang, → delay.