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.
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
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
The service was established by Congress as the main line of defense for children who are exploited online.
From Seattle Times • Apr. 22, 2024
They are the ship's main line of defence.
From BBC • Mar. 25, 2024
It was the main line from Venice to Trieste, with a high solid embankment, a solid roadbed and double track.
From "A Farewell To Arms" by Ernest Hemingway
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.
