E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Sheet Anchor.
That is my sheet anchor—my chief stay, my chief dependence. The sheet anchor is the largest and heaviest of all. The word is a corruption of Shote-anchor, the anchor shot or thrown out in stress of weather. Many ships carry more than one sheet-anchor outside the ship’s waist.
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“The surgeon no longer bleeds. If you ask him ‘why this neglect of what was once considered the sheet anchor of practice in certain diseases?’ he will …”—The Times.
