Green’s Dictionary of Slang

1. (US) a person of importance, the boss.

1899		Ade Fables in Sl. (1902) 24: I was just Thinking what chance have I got to grow up and be the Main Stem, like Mr. Jeffries.
1902		Guilelmensian (Williams Coll.) 289: Some one asked him if he had ever seen a baseball, to which he replied that he had been the Main Stem of the Prep. school team.
1904		Number 1500 Life In Sing Sing 256: Main Stem. Head person.
1949		Monteleone Criminal Sl. (rev. edn).

2. (also big stem) the main street of a town.

1900		Flynt & Walton Powers That Prey 250: One can complete investigations that have been begun in ‘the main stem’ of towns thousands of miles away.
1907		J. London Road 160: The kids began ‘battering’ the ‘main-stem’ for ‘light pieces,’ or, in other words, begging for money on the main street.
1916		J. Lait ‘Canada Kid’ in Beef, Iron and Wine (1917) 181: It’s got me wingin’, too. I keep right on workin’—I lift a boob for $106.60 on a mainstem caboose yesterday.
1923		N. Anderson Hobo 3: They call it ‘The Main Stem,’ a term borrowed from tramp jargon, and meaning the main street of the town.
1931		P.J. Wolfson Bodies are Dust (2019) [ebook] ‘Big Stem James,’ [...] a familiar figure on the ‘Big Street’.
1938		M. Rand ‘Clip-Joint Chisellers’ in Ten Story Gang Aug. 🌐 As gold diggers they could chisel nicer and dig deeper than any two chippies on the big stem.
1939		P. Cheyney Don’t Get Me Wrong (1956) 60: It is twelve o’clock an’ a sweet night, an’ I am walking down the main stem ponderin’.
1946		Mezzrow & Wolfe Really the Blues 138: Tin Pan Alley was soon to be the main stem in the music world.
1953		Mad mag. June–July 27: A dingy two-by-four office on the main stem.
1956		N. Algren Walk on the Wild Side 67: I go down the main stem and I’m on my way back to The Home by morning.
1962		Ragen & Finston World’s Toughest Prison 808: main stem – The main street or a town or city.
1972		O. Hawkins Ghetto Sketches 24: Saturday night ... any Saturday ... the main stem sizzles and crackles with the flicker of neon lights.
1993		I.L. Allen City in Sl. (1995) 41: The main drag or main stem originally was the main thoroughfare of hobohemias, such as the Bowery, rather than the principal and most central street of a town, such as Fifth Avenue or 42nd Street. But the terms in slang were generalized to the main street of a city, or to the main thoroughfare of some part of a large city.
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.

3. (US black) attrib. use of sense 2, stylish, sophisticated.

1928		W. Winchell Your Broadway & Mine 20 Nov. [synd. col.] The most interesting of the Main Stem topics at present is the Arnold Rothstein case.
1939		Pittsburgh Courier (PA) 29 Apr. 11/1: Mae Diggs [...] is being hired by a main stem nitery.
1968		T. Wolfe Electric Kool-Aid Acid Test (1969) 384: He has on tight black pants, black shark toe slip-on shoes, a soft black sweater and open-neck shirt . . . dressed Main Stem hipster, in short.

4. (US tramp) the most important street of a town in the context of tramp society and standards.

1927		W. Edge Main Stem 17: We are now on the ‘stem’ or ‘main stem’ or ‘main drag’ [...] The main stem is the principal street from the hobo’s point of view. It is not the main residential street; it is not the main business street; it is the hobo’s street [...] It is on this street that the homeless have put their stamp of approval.
1930		‘Dean Stiff’ Milk and Honey Route 209: Main stem – The chief hobo street in town.

5. Broadway, New York City.

1927		Morn. Call (Allentown, PA) 8 Dec. 10/5: Broadway is known as ‘The Main Stem’.
1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 252: apple (n.): the big town, the main stem, Harlem.
1993		I.L. Allen City in Sl. (1995) 41: The main drag or main stem originally was the main thoroughfare of hobohemias, such as the Bowery, rather than the principal and most central street of a town, such as Fifth Avenue or 42nd Street. But the terms in slang were generalized to the main street of a city, or to the main thoroughfare of some part of a large city. The theater district along Broadway was once called The Main Stem.

6. attrib. use of sense 5.

1942		W. Winchell On Broadway 31 Jan. [synd. col.] Loudspeakers in front of Main Stem music shops pouring out romantic tunes.
1952		W. Winchell On Broadway 18 Aug. [synd. col.] His wham click at the Capri is Main Stem gab.