c. 1300, "hard to manage, reckless, violent," from Old French estordi (11c., Modern French étourdi) "violent," originally "dazed," past participle of estordiir "to daze, stun, stupefy," from Vulgar Latin *exturdire, which some presume to be from Latin intensive prefix ex- + turdus "thrush." Barnhart suggests the notion is of thrushes eating grape remnants at wineries and behaving as if drunk (Italian tordo "thrush" also means "simpleton," and French has the expression soûl comme une grive "drunk as a thrush"). OED, however, regards all this as "open to grave objection." Century Dictionary compares Latin torpidus "dull."
Sense of "solidly built, strong and hardy" first recorded late 14c. Related: Sturdily; sturdiness. Sturdy-boots "obstinate person" is from 1762; a sturdy beggar in old language was one capable of work (c. 1400).