Definition of "cofferdam"

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

1851, Herman Melville, Moby-Dick

Downstream there was a small wooden cofferdam and when he woke there were naked children splashing in the pool there and he rose and wrapped his jacket about his waist and walked out along the bank where he could sit and watch them.

1992, Cormac McCarthy, All the Pretty Horses

Where the viaduct crosses the lake, the piles will be bored directly into the lakebed, using a cofferdam to hold back the water while the pier is built.

2022 January 12, “Network News: First pier cast for HS2's Colne Valley Viaduct”, in RAIL, number 948, page 10