The Collaborative International Dictionary of English v.0.48:

Dewar \Dew"ar\ (d[=u]"[~e]r), Dewar vessel \Dew"ar ves`sel\,
Dewar flask \Dew"ar flask\ [After Sir James Dewar, British
   physicist.]
   A double-walled glass vessel for holding liquid air, liquid
   nitrogen, etc., having the space between the walls exhausted
   so as to prevent conduction of heat, and sometimes having the
   glass silvered to prevent absorption of radiant heat; --
   called also, according to the particular shape,

   Dewar bulb,

   Dewar tube, etc.
      [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

Dewar flask
    n 1: vacuum flask that holds liquid air or helium for scientific
         experiments [syn: Dewar flask, Dewar]