Definition of "keyman" in English

noun

1. (dated) A telegraph operator.

   • Conscious of their importance, the 324 labor delegates marched bravely in and elected by acclaim as their president a onetime Ontario telegraph keyman, Senator Gideon Decker Robertson […]

2. (India) A workman who checks a railway track for faults, and who carries a keying hammer.

3. An employee of vital importance to a business.