linesman

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Football An official who marks the downs and the position of the ball and watches for certain violations from the sidelines.
2. n. Sports An official in various court games whose chief duty is to call shots that fall out of bounds.
3. n. Sports An official in soccer and other field games who indicates when the ball has gone out of bounds.
4. n. Sports Either of two officials in ice hockey who call icing and offsides, conduct face-offs, and call penalities.
5. n. See lineman.

Century Dictionary and Cyclopedia

1. n. Milit., a private in the line; an infantryman.
2. n. In Amer. foot-ball, one of the forwards; also, the man who has charge of the measurements of the distance gained and assists the umpire in various ways.
3. n. A workman engaged in the erection or maintenance of the line-wires of a telegraphic or telephonic system, or of electric circuits of any sort.

Wiktionary

1. n. soccer, dated An assistant referee.
2. n. tennis An official who calls shots that pitch out of bounds, and judges foot faults.
3. n. ice hockey An official whose primary task is to watch the blue line and determine when there has been an offside.
4. n. American football An official whose primary task is to determine whether there has been a line of scrimmage violation.
5. n. A person employed to work on electrical lines; a lineman.

GNU Webster's 1913

1. n. the official (in tennis or soccer) who watches the lines.
2. n. a person who installs or repairs electrical or telephone lines.

WordNet 3.0

1. n. official (in tennis, soccer, football, etc.) who assists the referee in some way (especially by watching for out of bounds or offside)
2. n. a person who installs or repairs electrical or telephone lines