Green’s Dictionary of Slang

1. the action of thrusting forward the abdomen or hips, as in a dance; thus bumper n., a striptease artist who performs this action; thus bump and grind under bump v.¹

1928		R. Fisher Walls Of Jericho 110: I’m going to get that bump-the-bump dance if it takes me the whole darn night!
1938		H.M. Anderson Strip Tease 16: The first teaser flashed a breast. A second topped her with a suggestive song. A third added the bump and the grind.
1951		Green & Laurie Show Biz from Vaude to Video 76: ‘Bumps’ were added to this, also the spinning of the breasts and the rump.
1957		L. Sobel 2 Apr. [synd. col.] A show full of [...] grinders, peelers, and bumpers [W&F].
1959		E. De Roo Go, Man, Go! 15: Then she gave a little bump. ‘Have one on me, shack-boy. My my, how frustrated you are.’.

2. dismissal, ‘the sack’.

1940		E. Pound letter 14 Mar. in Paige Sel. Letters (1971) 340: If a race neglects to create its own gods, it gets the bump.
1942		Berrey & Van den Bark Amer. Thes. Sl.

3. spontaneous, cursory sexual intercourse; thus bump and grind under bump v.¹

1982

G.V. Higgins Patriot Game (1985) 37: You got some whore lined up for nooners I assume, and then after the bump it’s back to the grind?

4. (US und.) in a pickpocketing team, one who knocks into the intended victim, distracting them from the actual pickpocket.

2012

L. Berney Whiplash River [ebook] Devane had kept his eye on the attaché case. He didn’t think the old man was really a bump. Who would try something that clumsy?