keyman

key +‎ man

keyman (plural keymen)

1. (dated) A telegraph operator.
   • 1932, Time (volume 19, part 2)

     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.
   • 1957, Pearce Shepherd, Andrew C. Webster, Selection of risks:

     A corporation may feel the need for life insurance on one of its keymen under a variety of circumstances.

   • 2000, Harvey C. Krentzman, The essentials of business management for profit, page 123:

     As the keymen learn how to handle confidential company information, the owner-manager can disclose more to them. In most very small firms, the keymen will be "working" bosses.

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