noun
sounding lead; plummet
A weight on a line used to measure water depth or to test vertical alignment. Technical term used in surveying, navigation, and construction.
測鉛を使って水深を測る。
Measure the water depth using a sounding lead.
昔の船は測鉛で海底の深さを調べた。
Old ships checked the depth of the seabed with a plummet.
Compound of 測 (measure) and 鉛 (lead), referring to a lead weight used for measuring. The term is a straightforward technical coinage.