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.
Lizzy Stroud and her husband Dave run self-catering accommodation in converted train carriages at stations on the Great Western Railway main line at St Germans and Harvey of Hayle, near St Ives in Cornwall.
From BBC • May 8, 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
A message The Associated Press left on the city’s Law Department main line seeking comment Monday wasn’t immediately returned.
From Seattle Times • May 27, 2024
The main line had been cleared and the first train rattled slowly through.
From "A Separate Peace" by John Knowles
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.
