howyoudaoicibaDictYouDict[how 词源字典]
how: [OE] How belongs to the large family of question-words which in Indo-European began with qw- (as in English quantity, query, etc). The phonetic descendant of this in prehistoric Germanic was khw-, which in modern English is represented by wh-. How itself comes from a West Germanic adverb *khwō formed from the base that also produced English what and who; like who it has lost its /w/ sound, but since who did not lose it until considerably later the spelling wh remains as a reminder of it.

The how! with which North American Indians supposedly greet each other is not the same word, incidentally. It is an imitation of a Sioux word, such as Dakota háo or Omaha hau.

=> what, who[how etymology, how origin, 英语词源]
how (adv.)youdaoicibaDictYouDict
Old English hu, from Proto-Germanic *hwo- (cognates: Old Saxon hwo, Old Frisian, Middle Dutch hu. Dutch hoe, German wie, Gothic hvaiwa "how"), from common PIE interrogative pronominal stem *kwo- (see who). How come? for "why?" is recorded from 1848. And how! emphatic, first recorded 1865. The formulation was common in book and article titles by then (such as The National Debt, and How to Pay It), but Pennsylvania writer Bayard Taylor, in whom it is first recorded, seems to regard it as a German or German-American expression.
how (interj.)youdaoicibaDictYouDict
Native American greeting, Siouxan (Dakota hao, Omaha hau); first recorded 1817 in English, but noted early 17c. by French missionary Jean de Brebeuf among Hurons as an expression of approval (1636).