Meaning

adjective marked by extreme intensity of emotions or convictions; inclined to react violently; fervid

adjective characterized by great force or energy

originBorrowed from Middle French vehement (modern French véhément; compare Italian veemente, Portuguese veemente, Spanish vehemente); or from Latin vehemēns (“vehement; very eager; ardent, furious, impetuous; emphatic”), probably from vē- (“lacking, too little”) + mēns (“mind; intellect; judgment, reasoning”).

Etymology from Wiktionary, CC BY-SA 3.0