Dictionary.net

• sh[=e]t'-angk'ur, n. the largest anchor of a ship, shot or thrown out in extreme danger: chief support: last refuge. [Shoot and anchor.]

1908 - Chambers's Twentieth Century Dictionary of the English Language
By Thomas Davidson

• n. The largest anchor of a ship, which, in stress of weather, is sometimes the seaman's last refuge to prevent the ship from going ashore; — hence, the chief support; the last refuge for safety.

1871 - The Cabinet Dictionary of the English Language