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
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
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
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
Network Rail has warned that the Midland Main Line will remain closed to East Midlands Railway and Thameslink services until the end of the week.
From BBC ● Jun. 24, 2026
In suburbs including Philadelphia’s Main Line, moms and dads are pleading with districts to rein in tech: “These electronics have ruined parenting.”
From The Wall Street Journal ● Jun. 22, 2026
Cardinale grew up in Villanova, Penn., an affluent suburb on Philadelphia’s Main Line, and attended The Haverford School, an all-boys prep school.
From The Wall Street Journal ● Jan. 16, 2026
The £26m project they'll be working on this Christmas is one of the biggest scheduled across the country: Hanslope Junction, a crucial part of the West Coast Main Line, which is wearing out.
From BBC ● Dec. 21, 2025
It’s on the prestigious Main Line, just twenty-five minutes outside Philadelphia, on a rolling campus surrounded by overgrown foliage.
From "The Other Wes Moore: One Name, Two Fates" by Wes Moore
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.
