a principal line or route of a railroad, as contrasted with a branch or secondary one.
a principal highway.
Slang.
a prominent and readily accessible vein of the body that may be used for a narcotic's injection.
the act of mainlining.
a fashionable residential district west of Philadelphia.
any fashionable district where socially prominent people live.
railways
the trunk route between two points, usually fed by branch lines
( as modifier )
a main-line station
a main road
First recorded in 1835–45
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
"The Severn Tunnel is the heartbeat of this main line, it's important in connecting communities on each side of the Severn so it's very important that it's operational and reliable."
From BBC • May 22, 2026
Warwickshire Police said its main line of inquiry was that a vehicle had hit the man and left the scene.
From BBC • Apr. 5, 2026
Pike followed the main line — called the trunk line — which had hoses branching off in other directions.
From Los Angeles Times • Mar. 11, 2026
The extensive corroborating evidence is just one way the prosecution is cutting off the defense’s main line of attack.
From Los Angeles Times • May 2, 2024
Railroad workers had laid a temporary track between the main line and the street so that the wagon could pull up next to the president's rail car.
From "Ambushed!" by Gail Jarrow
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
