mainline

Etymology

It is formed from English main + line, first as the noun main line, the principal line of a railway, recorded from 1841.^[2][3][4] The adjective is a use of that noun,^[2][4] and the verb either comes directly from it, in its slang sense of a principal vein into which drugs are injected, or is a back-formation from mainliner.^[2][3][5] Dictionary.com calls the verb an Americanism of 1935–40.^[6]

Earliest recorded meaning

Of or relating to the main line of a railway: 1879, in the Memoirs of a Station Master by E. J. Simmons.^[2]

Semantic evolution

The noun main line spread from railways to any principal route or channel (1845) and, in American slang, to a principal vein (1931) and to an injection of drugs into it.^[2][4] From this came the verb, to inject a drug intravenously: Etymonline dates it to 1934,^[3] the OED, Merriam-Webster and Green's Dictionary of Slang to 1938, when David Maurer listed it in a glossary of the narcotic addict's language.^[2][4][7] From 1971 it was used figuratively, of consuming something avidly as if it were a drug.^[2][4] The adjective followed a separate path: from the railway it came to describe the rich suburbs along the Pennsylvania Railroad's main line west of Philadelphia and their elite (1941),^[2][3] and, in the same year, anything principal, well established or conventional.^[2][4] From 1948 it was applied to the traditional Protestant denominations, as opposed to fundamentalist or evangelical ones.^[2] In American prison slang the mainline is the general convict population, outside the punishment cells, recorded from 1933.^[7]

Timeline

• 1879 – adjective, of a railway's main line.^[2]
• 1933 – in American prison slang, the general prison population.^[7]
• 1937 – adjective, of the injection of drugs into a vein.^[2]
• 1938 – verb, to inject a drug intravenously.^[2][4][7] Etymonline dates the verb to 1934.^[3]
• 1941 – adjective, of the Philadelphia Main Line or a similar elite.^[2]
• 1941 – adjective, principal, established, conventional.^[2][4]
• 1948 – adjective, of the traditional Protestant churches.^[2]
• 1971 – verb, figurative, to consume avidly.^[2]

Meanings

Verb

1. (slang) To inject a drug such as heroin directly into a vein: He had been mainlining for years before he sought help.^[4][2][5]
2. (figurative) To take in something eagerly and in large amounts, as if it were a drug: She mainlined the whole series in a weekend.^[4][2]

Adjective

1. Belonging to an established or dominant group; mainstream or conventional.^[4][2]
2. Of the traditional Protestant denominations, as opposed to fundamentalist or evangelical ones: mainline churches.^[4][2]
3. Of or relating to the main line of a railway.^[2]
4. (US, informal) Of or characteristic of the Philadelphia Main Line or a similar wealthy elite.^[2]

Word family

• mainliner

Related words

• main line
• main
• line
• mainstream

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s t u v w Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f g h i j k l Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
7. ^ a b c d Green, Jonathon (2010), Green's Dictionary of Slang, London: Chambers; digital ed. 2016–, https://greensdictofslang.com