What we now know as the thermos was invented in 1892 by British scientist Sir James Dewar, a scientist at Oxford University.
A German company marketed Dewar's invention, and soon thermos became the generic term for any container with a vacuum between an inner and outer wall that helps its contents retain their initial temperature (rather than cool or warm to the ambient temperature).
The American Thermos Bottle Company bought the trademark rights in the U.S., but never managed to stuff the language back into its bottle. After decades attempting to prohibit the generic use of thermos, the then-renamed American Thermos Products Company lost its trademark in court in 1962.
So where did the word come from? A contest: the winning submission recalled the Greek thermē, meaning heat.