I have some friends, and they say “Yo!” when I call them. I haven”t heard this response until quite recently (somehow), and I thought it was some word coined by rappers in their songs, and was adopted as a response by other people (like my friends, who happen to listen to rap).
So I was rather surprised, when looking this up on Wiktionary, I read:
(military slang) Present! Here!
Private Smith: Yo!
I thought to myself, “Obviously this ain’t coined by them rappers!”
Then, I saw a similar question on Yahoo Answers, with an answer stating (one link provided):
Yo is an American English slang interjection. The origins of the word may possibly be traced back to 14th century England. However, it was highly popularized after being commonly used among Italian Americans and African Americans in Philadelphia, Pennsylvania.
Clicking on the link provided, it turns out to lead to Answers.com. But the funny thing was, the new source included this information:
An exclamation used as a greeting, to express excitement, to attract attention, or as a general sign of familiarity (originating among young African-Americans). (1966–) .
I am inclined to think that the word yo came from the 14th century, but have no real evidence to say so. Can anyone provide solid stuff? That is, did it come from a military response, or a word used among young African-Americans in 1966?
Edit: I am asking specifically in relation to yo being used as a response/reply.