early 15c., from Old French vehement, veement "impetuous, ardent" (12c.), from Latin vehementem (nominative vehemens) "impetuous, eager, violent, furious, ardent, carried away," perhaps [Barnhart] from a lost present middle participle of vehere "to carry" (from PIE root *wegh- "to go, move, transport in a vehicle"). The other theory is that it represents vehe- "lacking, wanting" + mens "mind." Related: Vehemently.

Proto-Indo-European root meaning "to go, move, transport in a vehicle."

The root wegh-, "to convey, especially by wheeled vehicle," is found in virtually every branch of Indo-European, including now Anatolian. The root, as well as other widely represented roots such as aks- and nobh-, attests to the presence of the wheel — and vehicles using it — at the time Proto-Indo-European was spoken. [Watkins, p. 96]

It forms all or part of: always; away; convection; convey; convex; convoy; deviate; devious; envoy; evection; earwig; foy; graywacke; impervious; invective; inveigh; invoice; Norway; obviate; obvious; ochlocracy; ogee; pervious; previous; provection; quadrivium; thalweg; trivia; trivial; trivium; vector; vehemence; vehement; vehicle; vex; via; viaduct; viatic; viaticum; vogue; voyage; wacke; wag; waggish; wagon; wain; wall-eyed; wave (n.); way; wee; weigh; weight; wey; wiggle.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vahati "carries, conveys," vahitram, vahanam "vessel, ship;" Avestan vazaiti "he leads, draws;" Greek okhos "carriage, chariot;" Latin vehere "to carry, convey," vehiculum "carriage, chariot;" Old Church Slavonic vesti "to carry, convey," vozŭ "carriage, chariot;" Russian povozka "small sled;" Lithuanian vežu, vežti "to carry, convey," važis "a small sled;" Old Irish fecht "campaign, journey," fen "carriage, cart;" Welsh gwain "carriage, cart;" Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon."

"vehement or urgent desires," by 1711, from craving, verbal noun from crave.

"very hot, very ardent," 1830, as if from Latin *perfervidus, from per "completely" (see per) + fervidus "glowing, burning; vehement" (see fervid). Related: Perfervidly.

mid-14c., "act of crying aloud, a loud or vehement clamor," especially of indignation or distress, from out (adv.) + cry (v.). In metaphoric sense of "public protest," it is attested by 1911 in George Bernard Shaw.

"an emphatic assertion," 1550s, from Latin asseverationem (nominative asseveratio) "vehement assertion, protestation," noun of action from past-participle stem of asseverare/adseverare "affirm, insist on," from ad "to" (see ad-) + severus "serious, grave, strict, austere," which is probably from PIE root *segh- "to have, hold," on the notion of "steadfastness, toughness."