Merriam-Webster's Collegiate® Dictionary, 11th Edition
STALWART
I. adjective
Etymology: Middle English, alteration of stalworth, from Old English stǣlwierthe serviceable
Date: 15th century
marked by outstanding strength and vigor of body, mind, or spirit , see: strong stalwartly adverb stalwartness noun
II. noun
Date: 15th century
a stalwart person, an unwavering partisan