Green’s Dictionary of Slang

1. (US tramp) orig. of a horse, a young mule.

1871		Plumas National (CA) 6 May 1/2: ‘Hole that ar hoss down tu the yearth’ [...] ‘Wo, Shavetail.’ ‘Git a fiddil; he’s trying a jig’.
1885		Hicksville News (OH) 1 Jan. 2/2: The six-mule team of ‘shave-tails’ sidled steadily on.
1897		A.H. Lewis Wolfville 168: My off-wheel mule – a reg’lar shave-tail – is bad medicine.
1916		Honolulu Star-Advertiser (HI) 27 Nov. 2/1: ‘The army mule is a great institootion [...] I remember [...] a shavetail [etc].
1930		‘Dean Stiff’ Milk and Honey Route 213: Shavetail – Young mules.
1931		Irwin Amer. Tramp and Und. Sl. 167: Shavetail.–Originally,. in American Army slang, a Second Lieutenant [...] The name was correctly applied to the green mules received for Army use, as dealers shaved the animals’ tail for a good portion of its length, leaving a tuft of hair at the end.
1950		Salt Lake Trib. (UT) 21 Mar. 68/5: Unbroken [army] mules [...] were marked by clipping the hair on their tails [and] called ‘shavetails’ [...] those who received them would know that they were green and dangerous.

2. (US) an inexperienced person; a new lieutenant.

1884		River Press (Fort Benton, MT) 30 Apr. 7/3: X says there are too many ‘shave-tails’ coming into helena [...] When asked what he meant by ‘shave-tail,’ he said ‘those d — d tenderfeet that eat pie with a fork’.
1899		Bismarck Wkly Trib. (ND) 27 Oct. 6/3: The young men fresh from West Point [...] are known as ‘Shavetails’.
1900		O. Wister Jimmyjohn Boss and Other Stories 148: Casey gave him [...] the name of Napoleon Shave-tail, and had his whiskey again paid for by the sympathetic Schmoll.
1905		R. Beach Pardners (1912) 142: What are ye laughin’ at, ye shavetail?
1917		L.A. Times 22 Apr. III 22: A lieutenant just out of West Point is a ‘shave-tail,’ because he has just changed his long cadet coat for the service uniform.
1918		W.A. Livergood diary 18 Sept. 🌐 He reminded me of one of those hard shavetail which wear gold bar on thier [sic] shoulder straps.
1921		St Louis Post-Dispatch (MO) 4 June 12/5: They sat at a table in a cafe in Paris [...] with them was [...] a shavetail of the American army.
1939		T. Wolfe Web and the Rock 187: New-commissioned shavetails, proud and handsome with their silver bars and well-cut uniforms.
1947		(con. 1944) J.H. Burns Gallery (1948) 123: You loathe saluting me on the street. You think, that sonofabitch shavetail ...
1961		G.L. Coon Meanwhile, Back at the Front (1962) 169: That skinny shavetail said you wanted to see me.
1972		(con. 1916) G. Swarthout Tin Lizzie Troop (1978) 57: A shavetail for eleven years?
1981		Dly World (Opelousas, LA) 15 July 4/2: If you had to convince [...] one of those [...] shavetails, you were in trouble.
1990		Central New Jersey News (New Brunswick, NJ) 6 Aug. 5/2: Like young shavetails, middle management are going to have to learn.
2022		(con. late 19C) J. Nevins ‘Western frontier gay slang’ on Twitter 2 Mar. 🌐 ‘shave tail’ = a virgin.