What does dewar mean?
A dewar is an insulating container built around a simple but powerful principle: two walls separated by a vacuum, which dramatically slows heat transfer. This design allows a dewar to hold extremely cold liquids like liquid nitrogen or liquid helium for long periods without rapid evaporation, making it indispensable in physics labs, hospitals, and anywhere cryogenic materials are stored or transported. The word comes from Sir James Dewar, the Scottish chemist and physicist who invented the vacuum flask in 1892 while working on the liquefaction of gases. In scientific writing, "dewar" typically appears lowercase for the generic vessel — as in "a 25-liter liquid nitrogen dewar" — while "Dewar flask" honors its inventor. Outside technical settings most English speakers would simply say thermos, but within cryogenics, chemistry, and medical storage of biological samples, "dewar" remains the standard professional term.
nounA dewar is a vacuum flask: an insulating container with double walls separated by a vacuum, used to keep liquids very cold (such as liquid nitrogen) or very hot. The word is also capitalized as the surname of the Scottish physicist Sir James Dewar, who invented the vessel in 1892.
- An insulated double-walled vacuum container used especially for storing cryogenic liquids such as liquid nitrogen or liquid helium.
- (capitalized) The surname of Scottish physicist Sir James Dewar (1842–1923), inventor of the vacuum flask.
"The lab technician refilled the dewar with liquid nitrogen before storing the samples."
"Helium-4 was transferred carefully from the storage dewar into the experiment's cooling system."
"Each laboratory kept at least one spare dewar on hand in case a delivery of liquid nitrogen was delayed."
Standard regular plural; used when referring to multiple vessels.
"The storeroom held several dewars of varying sizes."
The humble thermos in your kitchen owes its existence to Sir James Dewar, who invented the vacuum flask in 1892 to store liquefied gases — and never patented it, losing a fortune.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dewar
The word "dewar" is an eponym, derived from the surname of Sir James Dewar (1842–1923), the Scottish physicist and chemist who invented the vacuum flask in 1892 during his research on liquefied gases. Because it originates from a proper name rather than an ancient root, it has no cognates in other languages or shared etymological relatives; related forms are limited to compounds such as "Dewar flask" and "Dewar vessel." The lowercase use of the eponym follows the common pattern by which inventors' names become ordinary nouns.
Related word forms
How dewar is actually used
In scientific contexts, "dewar" is usually written lowercase when referring to the generic container, though it derives from a proper name; capitalized forms such as "Dewar flask" are also common, particularly in older or more formal texts. Outside laboratories the everyday term is simply "thermos" or "vacuum flask," so "dewar" carries a technical register.
Easily confused with dewar
An ewer is a decorative jug or pitcher for water, while a dewar is an insulated vacuum container for keeping substances hot or cold.