Vehemence, n.
Etymology: [L. vehementia: cf. F. véhémence.]
1. The quality pr state of being vehement; impetuous force; impetuosity; violence; fury; as, the vehemence.
2. Violent ardor; great heat; animated fervor; as, the vehemence of love, anger, or other passions. I . . . tremble at his vehemence of temper. Addison.
Shades of meaning
Fernald has no entry of its own for vehemence; he lists it under enthusiasm.
Where he writes about it:
Against the hindrances of the world, nothing great and good can be carried without a certain fervor, intensity, and vehemence; these joined with faith, courage, and hopefulness make enthusiasm. — from enthusiasm