What is the origin of stalwart?

Stalwart “strong and brave; valiant” or “firm, steadfast, or uncompromising” is in origin a Scots form of Middle English stalworth “strong, sturdy, serviceable.” Stalworth has many variant spellings in Middle English because its second syllable was confused with the adjective worth “having monetary value.” In fact, stalworth comes from Old English stǣlwirthe “able to stand a person in good stead; serviceable (of ships).” Stǣl is probably a contraction of stathol “base, support, bottom (of a haystack)”; the Old English adjective suffix –wirthe, with the variants –wierðe, –wyrðe, –weorðe “good, worthy,” survives in modern English worth. Stalwart in the sense “serviceable” entered English before 900; the other senses date from the late 12th century.