to be on tenterhooks

from The Collaborative International Dictionary of English v.0.48
Tenter \Ten"ter\, n. [OE. tenture, tentoure, OF. tenture a
   stretching, spreading, F. tenture hangings, tapestry, from L.
   tendere, tentum, to stretch. See {Tend} to move.]
   A machine or frame for stretching cloth by means of hooks,
   called tenter-hooks, so that it may dry even and square.
   [1913 Webster]

   {Tenter ground}, a place where tenters are erected.

   {Tenter-hook}, a sharp, hooked nail used for fastening cloth
      on a tenter.

   {To be on the tenters}, {To be on the tenter-hooks} or {To be
   on tenterhooks}, to be on the stretch; to be in distress,
      uneasiness, or suspense. --Hudibras.
      [1913 Webster +PJC]
    

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