1 Mate: Ship ahoy!
2 Ponsonby: You’re not just yelling that for the ship spotting bonus, are you?
3 Mate: No, there really is a ship ahoy!
4 Ponsonby: Is “ahoy” to port or starboard?
4 Mate: It’s just... hoy! Over there!

Wikipedia's page on the word "ahoy" is astonishingly comprehensive, covering usage fo the word in multiple languages, including English, German, and several Baltic and Eastern European languages.

The word traces recorded origins as an interjection in Middle English and Middle High German in the 13th and 14th centuries, but of course it was probably in spoken use before this. "Ahoy" was picked up by sailors and incorporated in nautical parlance, where it is recorded in the 1700s. It seems to have more or less died out in general usage but been preserved by seafarers and became known as nautical jargon, from where it subsequently leaked back into common usage via stage plays, sea shanties, and literature.

Perhaps the most historically amusing anecdote regarding the word is that when Alexander Graham Bell invented the telephone there was no standard for how to greet a caller when picking up a ringing phone. Although eventually the word "hello" became standard (suggested by Thomas Edison), Bell initially favoured the picking up the phone and answering with a hearty "Ahoy!"

Try that with your friends next time they call!