From line + -man.

lineman (plural linemen)

1. A person who installs and repairs overhead cables (either power or telephone); a linesman.
   • 1966 March, Thomas Pynchon, chapter 6, in The Crying of Lot 49, Philadelphia, Pa.; New York, N.Y.: J[oshua] B[allinger] Lippincott Company, →OCLC ↗, page 135 ↗:

     […] or even, daring, spent the night up some pole in a lineman's tent like caterpillars, swung among a web of telephone wires, living in the very copper rigging and secular miracle of communication, untroubled by the dumb voltages flickering their miles, the night long, in the thousands of unheard messages.

2. (American football) A player who specializes in play at the line of scrimmage.
3. Someone who repairs railway tracks.