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
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 depletion of mangrove forests along the shoreline - the coast’s main line of defence against erosion - is to blame.
From BBC • Aug. 13, 2024
Bathtubs and showers cost a bit more, usually starting around $225, and a sewer main line is the most expensive, especially if there are a lot of roots blocking it up.
From Seattle Times • Jan. 22, 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.
