To hail with a cry of "ahoy".
1.(used as a call to hail another ship, attract attention, etc.)
1. (nautical) a hail used to call a ship or to attract attention Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollinsPublishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Cite This Source
1751, from a + hoy, a nautical call used in hauling. The original form of the greeting seems to have been ho, the ship ahoy!
Learn More about ahoy