θερμός

Greek thermós (θερμός) means 'hot,' from the Proto-Indo-European root *gʷher-, 'to heat' or 'to warm.' The same root produced Latin formus (warm), English warm itself (through Germanic), and Sanskrit gharma (heat). James Dewar, a Scottish chemist at the Royal Institution in London, built the first vacuum flask in 1892 to keep laboratory chemicals at stable temperatures. He used two glass walls with a vacuum between them — heat cannot cross a vacuum by conduction or convection. Dewar never patented the design. He considered it a laboratory tool, not a commercial product.

In 1904, Reinhold Burger, a German glass blower who had manufactured Dewar's flasks, realized their commercial potential. He held a contest to name the product. The winning entry was Thermos, from the Greek word for hot. Burger trademarked it, founded the Thermos GmbH company, and began selling vacuum flasks to the public. Dewar sued for credit and lost. The man who invented the technology got nothing; the man who named it got everything.

The Thermos bottle became one of the most successful consumer products of the 20th century. Expeditions to the North and South Poles carried them. Construction workers, schoolchildren, and office workers used them daily. The brand name became so ubiquitous that people used 'thermos' as a generic noun for any vacuum flask, regardless of manufacturer.

In 1963, a U.S. federal court ruled that 'thermos' had become a generic term — the public no longer associated it with a specific brand. King-Seeley Thermos Co. v. Aladdin Industries stripped the trademark protection. The company could still use 'Thermos' as a brand name, but it could not prevent competitors from calling their products thermoses. The word had escaped its owner, the way aspirin and escalator escaped theirs.