doughtyyoudaoicibaDictYouDict[doughty 词源字典]
doughty: [11] Doughty originally had the rather general sense ‘worthy, virtuous’ – ‘brave’ is a secondary specialization. It comes from late Old English dohtig, an unexplained variant of an earlier Old English dyhtig, which appears to have derived ultimately from a prehistoric Germanic *duhtiz ‘ability, capacity’. This in turn came from a verb *dugan ‘be able or strong’, which itself came into Old English and survived dialectally until the 19th century as dow ‘be able to do something’ or ‘thrive’.
[doughty etymology, doughty origin, 英语词源]
doughty (adj.)youdaoicibaDictYouDict
Old English dohtig "competent, good, valiant," from dyhtig "strong," related to dugan "to be fit, be able, be strong," and influenced by its past participle, dohte.

All from Proto-Germanic *duhtiz- (cognates: Middle High German tühtec, German tüchtig, Middle Dutch duchtich), from PIE *dheugh- "to be fit, be of use, proper" (cognates: German Tugend "virtue," Greek teukhein "to make ready," Irish dual "becoming, fit," Russian dužij "strong, robust"). Rare after 17c.; in deliberately archaic or mock-heroic use since c. 1800. If it had survived, its modern form would be dighty.