Green’s Dictionary of Slang

the buttocks, the posterior.

1849		W.C. Hall ‘Mike Hooter’s Fight with the “Bar”’ Spirit of the Times 10 Nov. (N.Y.) 452: He didn’t lay thar long ’fore the dogs they ’gan to chaw at his hide and kinder tickled the hind sights of the varmint.
1913		H. Kephart Our Southern Highlanders (1922) 102: I wish t’ my legs growed hind-side-fust [...] So ’s ’t wouldn’t bark my shins!
1942		New Yorker 10 Oct. 33: What’s she doing out in this rain, shoving along the beach on her hindside? [DARE].
1954		(con. 1920s–30s) J.O. Killens Youngblood (1956) 420: The crackers’ll take sides with him [...] And we’ll be right out on our hindparts.
1960		Bailey Resp. to PADS 20: Hindside [DARE].
1966		in DARE.
a.1969		‘One-Eyed Riley’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 251: I was a-sitting in my easy chair, / A-viewing the landlord’s daughter; / I took a notion in my head, / I’d like to feel her hindquarter.