Green’s Dictionary of Slang

1. (orig. US) usu. of people, an absolute replica (of); thus to be a dead ringer (for), to resemble completely.

1878		Weekly Register-Call (Central City, Colorado) 6 Sept. 1/4: The knight of La Mancha storming a wind mill, is a ‘dead ringer’, so to speak, for Windy Bill riding down a phalanx of Mexicans on a long-eared mule .
1885		St Paul Dly Globe (MN) 3 Nov. 5/4: Speaking of Mr Schurmeier, he is almost a dead ringer for Elwyn Barron.
1888		St Paul Dly Globe (MN) 22 June 2/1: Isn’t he a dead ringer for Puck’s pictures of him?
1891		N.Y. Sporting Times 4 July 10: Homan, Chicago’s new catcher, is a ‘dead-ringer’ for Anson—looks as much like Adrian as though he were his brother.
1902		E. Townsend Chimmie Fadden and Mr Paul 58: Duchess passes him out a swell bow what was a dead ringer for de style of bow dat Widdy gives.
1916		J. Buchan Greenmantle (1930) 308: Now you’re in these pretty clothes you’re the dead ringer of the brightest kind of American engineer.
1924		C.E. Mulford Hopalong Cassidy Returns 16: Dead ringer, even to yore hoss. Shore you ain’t him?
1935		(con. 1920s) J.T. Farrell Judgement Day in Studs Lonigan (1936) 642: The fellow was a dead ringer for Abie Kabibble.
1946		B. Cerf Anything For a Laugh 95: If it weren’t for the mustache, you’d be a dead ringer for my wife.
1953		B. Behan Scarperer (1966) 58: He’s certainly a dead ringer for the Limey.
1964		H.S. Thompson letter 31 Jan. in Proud Highway (1997) 436: I have dug into Franz Fanon and I think he is a dead ringer for the real thing.
1978		P. Theroux Picture Palace 302: ‘You mean it’s not Pound?’ ‘No, but it’s a dead-ringer.’.
1989		Kirk & Madsen After The Ball 299: Numerous frightened gay men reported having sex with this man – or a dead ringer.
1989		M. Walker How to Kiss a Crocodile 67: Chester was a dead ringer for Friar Tuck, with a horseshoe head of greying hair.
1993		K. Lette Foetal Attraction (1994) 167: She looks like me. [...] A dead ringer.
2000		Guardian G2 13 Mar. 26: A procession of alleged dead ringers gave us their versions of the rich and famous.
2015		P. Beatty Sellout (2016) 88: The sign was a dead ringer for any of the other ‘traffic control devices’ one sees.

2. a certainty.

1889

Rock Is. Dly Argus (IL) 24 June 4/1: It was a dead ringer that the man who ran against the wire would be shot.