Green’s Dictionary of Slang

(a) in fig. use of sense 2b, a bet, usu. spontaneous and unthought-out.

1867		J. Greenwood Unsentimental Journeys 183: He took a deliberate ‘header,’ trusting to the ‘Betting Man’s Guide’.
1884		W.C.Russell Jack’s Courtship Ch. vii: ‘Miss Hawke,’ said I, plucking up my heart for a header and going in, so to speak, with my eyes shut and my hands clenched [F&H].

(b) a head-first dive, usu. into water.

1856		Inside Sebastopol 297: These excellent public baths look delicious [...] we may surely shut the door and take a header.
1864, 1867, 1870		Hotten Sl. Dict.
1867		Sportsman 15 Oct. 2/1: [in. fig. use] Notes on News [...] He takes the most confident ‘headers’ into the deepest mysteries.
1868		Sporting Gaz. (Londson) 11 Jan. 13/3: [A] ‘header’ into a brook.
1871		Sportsman (London) ‘Notes on News’ 1 Feb. 2/2: [O]ne or other of them might induced take a ‘header’ which would result in the smashing of some of his ribs.
1879		C.J. Kickham Knocknagow 89: Then he cursed his stupidity for never having thought of taking a ‘header’ into a bog-hole, and remaining there with only his nose above water till they had passed.
1880		Bulletin (Sydney) 31 Jan. 3/3: He explained to them the utter uselessness of baptism by sprinkling, […] and clearly proved that salvation was to be attained by nothing less than a ‘header’ or a ‘dip.’.
1881		Bulletin (Sydney) 21 May. 4/2: This will prevent the annoyance often experienced [...] on the present bicycles, when the little wheel takes a fancy to climb up the rider’s back, and failing, leaves him to study astronomy on the sidewalk, after a ‘header’ and a few weals from the wheels.
1895		Crowe Aus. Sl. Dict. 35: Header, to plunge head foremost into the water.
1899		‘Pot’ & ‘Swears’ Scarlet City 174: I have been [...] wondering when you intended to take your header through the plate glass.
1900		Bulletin (Sydney) 24 Feb. 11/1: The fish was dozing peacefully in about 4ft. of water when a lady bather took a header and landed on his back.
1918		Kia Ora Coo-ee 15 June 5/1: I went for a swim in the Dead Sea. Shut my eyes and took a header, but to my surprise, still found myself on top.
1920		Bulletin (Sydney) 12 Feb. 28/2: [S]omeone gave the horses a sly cut with the whip and hiis Honor took a header .
1928		M. Meredith ‘The Human Head in Sl.’ in AS III No 5 408: To take a ‘header’ is to fall headforemost, headfirst, or headlong.
1937		J. Curtis There Ain’t No Justice 99: ‘I took a header off of Hammersmith Bridge and drowned meself.’ ‘Yerce. You look like it.’.
1940		M. Marples Public School Slang 69: header: a jump head first (1870): nopw general.
1949		N. Algren Man with the Golden Arm 89: The cashier’s face white as a split apple [...] as she took a header.
1955		B. Schulberg On the Waterfront (1964) 65: I comes out the swingin’ door of McCarty’s [...] an’ do a header into a snowbank.
1964		J. Thompson Pop. 1280 in Four Novels (1983) 369: I almost took a header as I came out.
1970		San Diego Sailor 44: I [...] took a clean header through the surf.
1982		G.V. Higgins Patriot Game (1985) 72: This guy could always take a header when it really counted.
1990		J. Wambaugh Golden Orange (1991) 248: The former marine [...] staggered into the men’s room, where he took a header.
1999		N. Cohn Yes We have No 288: Someone took a header down the stairs.
2001		A. Sillitoe Birthday 201: I thought she was going to do a header through the windscreen.

(c) a social decline.

1920

T. Thursday ‘Mr. Mister’ in All-Story Weekly 22 May 🌐 There’s something phony about all those Mister guys. I never bumped one yet who didn’t take a header downhill sooner or later.

(d) one who jumps, usu. for the purposes of suicide, off a high building, bridge etc.

1990

S. Morgan Homeboy 207: Just spotted a header off Coit Tower.