Sheet anchor
Sheet anchor , transitive verb
[Old English scheten to shoot, Anglo-Saxon sceótan; compare Old English shoot anchor. See Shoot, transitive verb]
1.
(Nautical) A large anchor stowed on shores outside the waist of a vessel; -- called also waist anchor. See the Note under Anchor.
2.
Anything regarded as a sure support or dependence in danger; the best hope or refuge.