cofferdam

noun

Etymology: From coffer + dam. The dental dam sense was introduced in English by dentist Sanford Christie Barnum at New York City in 1864 (by metaphor), but after his century it was maintained only in languages other than English (for example, German Kofferdam as a loanword from 19th-century English).

1. A temporary watertight enclosure used to create a dry foundation for building bridges and other structures over water.

   “The contractor for the cofferdams, &c., was an Englishman, as were the principle workmen, and all the machinery has been supplied from England.”

   “He stood full six feet in height, with noble shoulders, and a chest like a coffer-dam.”

2. An empty space that acts as a protective barrier between two floors or bulkheads on a ship.
3. Synonym of dental dam (“barrier to keep the teeth dry during dental work”) (dental sense).

   “I refer to Dr. Barnum, who has given us the coffer-dam. I cannot detain you while I describe the immense benefit which his application of a very simple material has conferred on the public.”

   “Dr. La Roche then first we are informed made the claim that he knew of and used rubber for a coffer dam prior to Barnum.”