cofferdam

Meanings

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

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).