Definition of "ahoy"

While he was thus occupied, a voice, still more uncouth than the former, bawled aloud, ‘Ho! the house, a-hoy!’

1751, Tobias Smollett, The Adventures of Peregrine Pickle

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[rosby] Lincoln, chapter VII, in Mr. Pratt’s Patients, New York, N.Y., London: D[aniel] Appleton and Company

Lawsuits, ahoy! […] Towns can regulate use of their beaches. But what about the waters offshore?

1989, Forbes, volume 143, numbers 5-7, page 74

Catalytic converters ahoy – Zeppelin's latest is one of those high-rev 3D driving games that simulates racing tracks from all over the world.

1992, Championship Run (video game review) in Your Sinclair issue 75, page 61