early 15c., from Middle 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" (see vehicle). The other theory is that it represents vehe- "lacking, wanting" + mens "mind." Related: Vehemently.