plumb
n. C1 Advanced US //ˈpɫəm// UK //plˈʌm// plumb
n. a heavy metal weight used to measure the depth of water. You drop it into the sea to see how deep the water is.
n. a heavy lead weight used for measuring the depth of water. Often used in nautical contexts to determine the depth of a ship's keel or the depth of the sea.
The sailor dropped the plumb into the water.
Before anchoring, the captain lowered a plumb to check the depth of the harbor floor.
By measuring the time it took for the plumb to reach the seabed, the navigator could estimate the depth with a high degree of accuracy.
From Middle English plumbe, plumme, from Old French *plombe, from Latin plumba, plural of plumbum.