Bring your a-se to an anchor, i.e. sit down. To let go an anchor to the windward of the law; to keep within the letter of the law. Sea wit.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Anabaptist * AnglersNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes