thoughyoudaoicibaDictYouDict[though 词源字典]
though: [12] English borrowed though from Old Norse thōh, and by the end of the 15th century it had virtually wiped out the related native form, which went back to Old English thēah. Both came from a prehistoric Germanic adverb formed from the demonstrative base *tha- (source also of English that, there, etc) and a suffix meaning ‘and’. Modern Germanic relatives include German and Dutch doch.
=> the[though etymology, though origin, 英语词源]
though (adv., conj.)youdaoicibaDictYouDict
c. 1200, from Old English þeah "though, although, even if, however, nevertheless, although, still, yet;" and in part from Old Norse þo "though," both from Proto-Germanic *thaukh (cognates: Gothic þauh, Old Frisian thach, Middle Dutch, Dutch doch, Old High German doh, German doch), from PIE demonstrative pronoun *to- (see that). The evolution of the terminal sound did not follow laugh, tough, etc., though a tendency to end the word in "f" existed c. 1300-1750 and persists in dialects.