sheet anchor

Nautical. a large anchor used only in cases of emergency.

a final reliance or resource, as when in danger.

Origin of sheet anchor

First recorded in 1485–95

Poetry, History, Science, are the three strands of the cable by which the vessel shall ride—Religion being the sheet-anchor.

Blackwood's Edinburgh Magazine, Vol. 68, No 420, October 1850 |Various
Quinine, however, which is the sheet-anchor (so to speak) of African travellers, saved her.

Some Heroes of Travel |W. H. Davenport Adams
We have trusted to it as to the sheet-anchor of our safety, in the stormy times of conflict with a foreign or domestic foe.

Key-Notes of American Liberty |Various
He clung to all three, he grappled them to him; they were his sheet-anchor and his pole-star.

The Scapegoat |Hall Caine

We lost one man from the starboard forechains, by his getting caught in the buoy-rope, as we let go a sheet-anchor.

Ned Myers |James Fenimore Cooper

sheet anchor

nautical a large strong anchor for use in emergency

a person or thing to be relied upon in an emergency

C17: from earlier shute anker, from shoot (obsolete) the sheet of a sail