IPA: /ˈliːdz.mən/
KK: /ˈlɛdzˌmæn/
A person who uses a lead line to measure the depth of water, especially in nautical contexts.
The leadsman carefully measured the depth of the water to ensure safe navigation.
Leadsman → The word is formed from "lead" (from Old English *lædan*, meaning to guide or bring) and "man" (from Old English *mann*, meaning a person). A leadsman is a person who guides or directs, especially in navigation or piloting.
Think of someone who 'guides' ('lead') others — that's why a leadsman is a person who helps direct or navigate.