ridgling, n. — Green’s Dictionary of Slang

ridgling n.

[‘an animal that has been imperfectly castrated (originally also: spayed), or whose genitals are not properly developed; esp. a male animal (ram, bull, stallion, etc.) with only one testicle’ (OED); see rig n.⁵ +SE ridgel, an animal with only one testicle]

an impotent male.

1672

M. Atkins Cataplus 7: For he alas! was impotent; / In short, he was another such thing / As waggish people call a ridgling.