Sheet anchor

from WordNet (r) 3.0 (2006)

sheet anchor
    n 1: spare anchor for use in emergency [syn: {sheet anchor},
         {waist anchor}]

from The Collaborative International Dictionary of English v.0.48

Sheet anchor \Sheet" an"chor\ [OE. scheten to shoot, AS.
   sce['o]tan; cf. OE. shoot anchor. See {Shoot}, v. t.]
   1. (Naut.) A large anchor stowed on shores outside the waist
      of a vessel; -- called also {waist anchor}. See the Note
      under {Anchor}.
      [1913 Webster]

   2. Anything regarded as a sure support or dependence in
      danger; the best hope or refuge.
      [1913 Webster]