What is the etymology of hi)?

Answer 1

It is a grammatical shortening or grammaticalization of "How are you?" resulting from habitual use. Hiya (How you) served as an intermediate form. It developed in the course of the 18th century with hiya apearing in recorded text as early as 1940, though it likely was in use before then.

Answer 2

The word "hi" is an informal greeting or a simple way to get someone's attention. It is derived from an English variant of the word "hey," which has been in use since the 1400s. "Hi" is believed to have originated as a shortening of "hey" and has become a commonly used greeting in modern English.