An Etymological Dictionary of Astronomy and Astrophysics

Occurring within a short time; happening speedily; moving or acting with great speed; swift (Dictionary.com).

Etymology (EN): From L. rapidus “tearing away, seizing, swift,” from rapere “to hurry away, seize, plunder;”

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;”
PIE base *(s)teud- “to thrust, to beat”).