Green’s Dictionary of Slang

nards n.

1. (US) male genitals [? SE gonads].

[US]Current Sl. IV:3–4 (1970) 21: Nard, n. Testicle.
Online Sl. Dict. [Internet] nards n 1. testicles, balls. (‘I got kicked in the nards.’).
[US](con. 1964–8) J. Ellroy Cold Six Thousand 275: Pete kicked him. Pete nailed his nards good.

2. (US) the female breasts.

P. Munro U.C.L.A. Sl. II 61: Nards [...] breasts.