from The American Heritage® Dictionary of the English Language, 4th Edition
- interj. Informal Used to express greeting. See Regional Note at hey.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- interj. A friendly, informal, casual greeting said when meeting someone.
- adj. Informal spelling of high, often hyphenated.
- n. "Hi" or similar greeting.
American English (first recorded reference is to speech of a Kansas Indian), originally to attract attention, probably a variant of Middle English hy, hey (circa 1475) also an exclamation to call attention. (Wiktionary)