Avast
/əˈvæst/
Definition 1 of 1
Pro Tip 1/3Nautical Origin
Originally used by sailors, it's not commonly heard outside of old nautical contexts or pirate stories. 
Avast! Secure the mainbrace before the storm hits!
Pro Tip 2/3Used to Interrupt
It's a way to abruptly stop someone or something, much like shouting 'Stop!' or 'Wait!' 
Avast! That's the wrong direction!
Pro Tip 3/3Archaic Usage
It's an old-fashioned term, so using it in everyday conversation might confuse people. 
Avast! No one speaks like that anymore.