Green’s Dictionary of Slang

1. (also rough nut, tough cud) a person who is difficult, obstinate or dangerous to deal with.

1862		E.W. Pearson Letters from Port Royal 81: There are a great many men of twenty-five to forty, ‘tough-nuts’ many of them.
1882		Nat. Police Gaz. (NY) 18 Mar. 2/1: Sindram is the toughest nut the Tombs keepers ever fell in with. A murderer who philosophizes on death and welcomes the hangman's noose is a terrifying character.
1894		Mirror of Life 8 Sept. 2/4: Jigsy Mcduff: ‘Is he is tough nut?’ Slob McTerrigan: ‘Tough? Wy, if he was to be run over be a bus, it wouldn't knock de ashes off de end of his cigarette’.
1901		Sydney Sportsman (Surrey Hills, NSW) 6 Nov. 4/1: Some of the toughest and hardest nuts sinful Sydney contains — men who would not trust their dad with a deener.
1907		J.W. Carr ‘Word-List from Hampstead, N.H.’ in DN III iii 203: tough cud, n. A hard character.
1908		Gem 17 Oct. 17: To tell you the truth, Merry, he’s a tough nut.
1918		L.M. Staley letter 6 Aug. at www.u.arizona.edu/~rstaley 🌐 He is a rather rough nut, but not as bad as some of this crowd.
1929		‘Ellery Queen’ Roman Hat Mystery 221: I know well enough you’re a tough nut, Inspector!
1939		A. Bessie Men in Battle 69: He is real dirty but hard as nails. ‘Great kid,’ the men say, ‘a tough nut.’.
1948		A. Wright Under the Whip 7: Andrew seems to be quite a tough nut when he gets down to talking business.
1959		C. MacInnes Absolute Beginners 141: From now on I’m going to be a tough, tough nut, and if she thinks she can hurt me, she’s bloody well mistaken.
1966		Analog Science Fiction/Science Fact 70: ‘You’re looking for trouble, O’Hare — this Farquhar is a tough nut.’ [...] ‘O’Hare is a tough nut, too, and can take care of himself.’.
1985		J.B. Sanford Color of the Air 146: ‘I thought you were a tough nut.’ ‘Oh, I am,’ you’d say. ‘I chew Star Navy and spit.’.
1992		M. Coleman Fatty 89: Even Terry Randall told me he was a real tough nut.
1999		Indep. 26 Sept. 29: But they are tough nuts all the same.
2000		Guardian G2 23 Mar. 22: I was tickled by the story of a tough nut [...] who had to be served a summons.
2000		S. Maloney Big Ask 56: Big Bob was a legend. A rough-nut among the silvertails. The man they couldn’t root, shoot or electrocute.
2006		D. Winslow Winter of Frankie Machine (2007) 84: Abe doesn’t need to be asked twice. Patty’s going to be a tougher nut.
2014		Ruderman & Laker Busted 201: Barbara had a knack for cracking tough nuts. She could have broken Al Capone.

2. attrib. use of sense 1.

1997

B. Lefkowitz Our Guys 149: Richie, a tough-nut kid. He was better than anything else we had. And he did an admirable job. Above-average toughness.