trunk line noun3 •A main railway line which usually forms the backbone of a rail network.But the states were generally concerned with the location of trunk lines and left it to cities and counties to worry about branch lines. — 1987 •The main line of a canal, from which other sections diverge. •A main telephone line.Then he put a trunk line phone call through to the nearest township and asked the Police to send someone out as soon as possible. — 1943 formstrunk lines
