From Anu Garg's A.Word.A.Day, now featuring words related to pirates:
avast (uh-VAST) interjectionThe word avast furnishes the name of avast!, an excellent anti-virus program.
Stop (used as a command to stop or desist).
[From Dutch hou vast (hold fast), from houd vast.]
"The best part, though, is the music. It dips and swells in the game right along with the action. Avast, there's treasure here!"
Vance Jordan and Melissa L. Jones, "Madden NFL Steps Up the Play," Arkansas Democrat-Gazette, Aug 27, 2006.
Link: avast! Home Edition, free for home and non-commercial use