hi

Etymology 1

American English. First recorded reference is to speech of a Kansas Indian (1862); originally to attract attention, probably a variant of Middle English hey, hy (circa 1475). Also an exclamation to call attention. See hey.

intj

1. A friendly, informal, casual greeting said upon someone's arrival.
   Hi, how are you?
   I just dropped by to say “hi”.
   Anna: Pete, hi! Hi, we are here! — Pete: Hi, Anna! Hi, Marsha! — Anna: Hi! — Pete: How are you two? — Marsha: I am great! Audio (US) (file) 2016, VOA Learning English (public domain)
2. An exclamation to call attention.
   I made a speaking trumpet of my hands and commenced to whoop “Ahoy!” and “Hello!” at the top of my lungs. […] The Colonel woke up, and, after asking what in brimstone was the matter, opened his mouth and roared “Hi!” and “Hello!” like the bull of Bashan. 1913, Joseph C. Lincoln, chapter 7, in Mr. Pratt's Patients
   'Come back now!' shouted Sam. 'Hi! Come back!' But Gollum had vanished. 1954, J. R. R. Tolkien, The Two Towers
3. (dated) Expressing wonder or derision.

noun

1. The word "hi" used as a greeting.
   I didn't even get a hi.

Etymology 2

From high.

adj

1. Informal spelling of high, often in hyphenated terms.
   Get hi-quality videos here!