official (in tennis, soccer, football, etc.) who assists the referee in some way (especially by watching for out of bounds or offside)
同义词：linesman
a person who installs or repairs electrical or telephone lines
同义词：electricianlinemanlinesman
英汉双解大词典
linesman/ˈlaɪnzmən/star1TEM8(linesmen)
1.
N-COUNT（可数名词）
A linesman is an official who assists the referee or umpire in games such as football and tennis by indicating when the ball goes over the lines around the edge of the field or court. 边线裁判员