late 14c., "resolute, determined," Scottish variant of stalworth, from Old English stælwierðe "good, serviceable," probably a contracted compound of staðol "base, foundation, support; stability, security" (from Proto-Germanic *stathlaz, from PIE root *sta- "to stand, set down, make or be firm;" see stet) + wierðe "good, excellent, worthy" (see worth). Another theory traces the first element of stælwierðe to Old English stæl "place," from Proto-Germanic *stælaz.