Definition of "vehement"

Yet the Fiends ſeemed to come nearer and nearer, but when they were come even almoſt at him, he cried out with a moſt vehement voice, I will walk in the ſtrength of the Lord God; ſo they gave back, and came no further.

1678, John Bunyan, The Pilgrim's Progress from This World, to That Which is to Come: Delivered under the Similitude of a Dream wherein is Discovered, the Manner of His Setting Out, His Dangerous Journey; and Safe Arrival at the Desired Countrey, London: Printed for Nath[aniel] Ponder at the Peacock in the Poultrey near Cornhill, page 79

Amy shook her head, vehement. "The vine didn't kill them. The Mayans did. They tried to flee and the Mayans shot them. The vine just claimed their bodies once they'd been shot. There's no thought involved in that. No—"

2006, Scott [Bechtel] Smith, The Ruins: A Novel, New York, N.Y.: Alfred A. Knopf, page 236