Green’s Dictionary of Slang

(US) to castrate, also used fig.

1916		H.N. Cary Sl. of Venery.
1950		Goldin et al. DAUL 146/2: Nut. To castrate; to sterilize one by surgical operation; deliberately to mutilate by castration.
1959		C. Himes Crazy Kill 129 You and me, baby, we’re going to nut him together.
1964		in E. Cray Erotic Muse (1992) 124: He offered half his kingdom / And the hole of Queen Hortense / To any loyal Briton / Who would nut the King of France.
1991		O.D. Brooks Legs 4: ‘Don’t come any closer, you old fart,’ I said, brandishing the knife wildly. ‘I’ll nut you so quick you’ll think you were born gelded.’.