I had assumed that "hi" was a somehow abbreviated form of "hello," but though both of these words appear to have originated from a noise to attract attention, hi actually predates hello. These words both appeared in the mid- to late 1800s, and seem to be primarily American usage. Does anyone know what Americans used for greetings prior to this time period?
Update on 9/10/11:
Although I have come to feel that "how do ye" and its variant "howdy" are most likely the common greetings in the early days of America, part of the difficulty in assessing this is the lack of recorded everyday speech. I was also unaware that "howdy" was used anywhere other than the US South prior to the 1800s, but the OED begs to differ (if someone has the citation for this, please feel free to link it).
There was considerable discussion in chat about the problem of researching common conversational speech, and during the course of that discussion, I realized that probably the best place to look would be plays, since they involve dialogue that might represent a "natural" conversation.
After a lot of searching through early American plays, I came across "holla" used as a greeting in the early American drama The Contrast by Royall Tyler. It was written and performed c. 1759, and its setting is contemporaneous New York City, therefore this greeting is probably an example of natural speech.
Interestingly, I did not find any instances of any other greetings. However, finding plays that were actually set in America in the 1700s and were also written around that period proved difficult.
Best Answer
How do ye / How do you do / Howdy?
From the etymology.com page on howdy:
Note that a search for "how do you do" in the Corpus of Historical American English (COHA) (1810s - 2000s) in particular brings results that are from the early 1810s (see number of occurrences per decade below). This supports that the usage of "how do you do" precedes the year in which Americans started greeting with "hi" according to etymonline.com (1862).
Similar searches in the COHA for "how do ye do" and "howdy" support that also their usage was prior to when "hi" started being used as a greeting.
Hal / Hail
Disclaimer: no evidence that these words were used in America. What follows is more like an interesting note on the history of greetings in English:
The book Speech acts in the history of English dedicates an entire chapter to greetings in English language history. Among the greetings that it covers, I would say that the closest one to hi! in spelling and usage is hail! The author describes hail as the Middle English daughter form of the Old English interjection hal. Hal! would literally mean health!.
You can browse the book here in Google Books.