Green’s Dictionary of Slang

1. to study hard.

1833		H. Smith Gale Middleton 1 37: It’s all owing to your grubbing so much in your study, and poking and poring over those plaguy books.
1848		Amherst Indicator in Hall (1856) I 233: I can grub out a lesson in Latin or mathematics as well as the best of them.
1856		B.H. Hall College Words (rev. edn) 255: Hobbies are used by some students in translating Latin, Greek, and other languages, who from this reason are said to ride, in contradistinction to others who learn their lessons by study, who are said to dig or grub.
1883		T.B. Reed Willoughby Captains (1887) 76: ‘Gully's no good as master of a house; he's always grubbing over his books’.
1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 40: grub, v. Equivalent of to bone or to grind.
1920		Ade Hand-made Fables 113: [He] decided to chop on the Money-Grubbing.
1933		J. Conroy Disinherited 196: I did know many clerks who had grubbed for years without getting anywhere.
1952		Lait & Mortimer USA Confidential 1: We grub for fifty-cent dollars which are snatched away from us by the talons of an insatiable horde of harpies.
1967		Current Sl. I:4 1/2: Grub, v. To study very hard.

2. to kiss passionately.

1966		Current Sl. I:3 3/2: Grub, v. To kiss; to pet.
1979		Eble Campus Sl. Mar. 4: grub – to kiss passionately.
1985		Eble Campus Sl. Fall 5: grub – kiss someone excessively (especially in public).
1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Grub (verb) To kiss, pet, pet heavily; to make out.

3. to have sexual intercourse.

1966		Current Sl. I:3 3/2: Grub, v. [...] to have sexual intercourse.
1984		Eble Campus Sl. Mar. 3: grubbin’ – any type of sexual activity: Let’s get drunk and grub.
1996		Eble Sl. and Sociability 41: Additional examples can be found in many subject areas, particularly in terms for [...] sex (boff, bong, bonk, bop, bump uglies, grub, and pork).