coffer dam

Noun

cofferdam (plural cofferdams)

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.1847, editorial staff, “Enormous Suspension-Bridge”, in Scientific American, series 1, Volume 3, Issue 9, page 65

   Synonyms:

   coffer, caisson

2. An empty space that acts as a protective barrier between two floors or bulkheads on a ship.
3. (obsolete) 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.1874 March 2, Edwin Sercombe, Esq., “Dental News and Critical Reports. Odontological Society of Great Britain. General monthly meeting and conversazione.”, in British Journal of Dental Science...

   Synonyms:

   dental dam