early 15c., impetous "rapid movement, rush;" 1640s, with modern spelling, "force with which a body moves, driving force," from Latin impetus "an attack, assault; rapid motion; an impulse; violence, vigor, force;" figuratively "ardor, passion," from impetere "to attack," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + petere "aim for, rush at" (from PIE root *pet- "to rush, to fly").
c. 1400, "absence of storm or wind," from the adjective or from Old French calme, carme "stillness, quiet, tranquility," or directly from Old Italian (see calm (adj.)). Figurative sense "peaceful manner, mild bearing" is from early 15c.; that of "freedom from agitation or passion" is from 1540s.
Aftir the calm, the trouble sone Mot folowe. ["Romance of the Rose," c. 1400]
"relating to or pertaining to prophecy or divination," 1836, from Greek mantikos "prophetic, oracular, of or for a soothsayer," from mantis "one who divines, a seer, prophet; one touched by divine madness," from mainesthai "be inspired," which is related to menos "passion, spirit," from PIE *mnyo-, suffixed form of root *men- (1) "to think," with derivatives referring to qualities and states of mind or thought. Related: Mantical (1580s).