Sterilize, castrate, spay, emasculate, alter, mutilate, geld, caponize mean to make incapable of producing offspring.
Sterilize, the most general of these terms, is applicable to both human beings and animals and is used whether the end is attained accidentally (as by undue exposure to X rays which kill germ cells) or deliberately (as by a surgical operation which prevents the germ cells from reaching the site where fertilization can occur or by removal of the gonads).
Sterilize often suggests a legalized procedure undertaken to prevent the reproduction of undesirables (as imbeciles and habitual criminals); the term does not imply physical disfigurement and does not in itself necessarily imply interference with the capacity for copulation.
Castrate, a narrower term than sterilize , means to deprive of the testes, the male reproductive glands. It is used of both human beings and animals and usually implies a surgical procedure and a loss of libido as well as of procreative power. By extension castrate may also mean to deprive of the ovaries, the female reproductive glands, and therefore is often used in place of spay, the specific term for this operation.
Emasculate is often preferred to castrate when the reference is to human males and especially when there is the intent to stress the loss of virile or masculine qualities.
Alter may replace castrate especially in reference to domestic pets and when an ambiguous or euphemistic term is appropriate.
Mutilate (see also MAIM ) is sometimes substituted for castrate especially when the intent is to convey strongly the idea of physical disfigurement or violence or when a euphemism is desired.
Geld, meaning to castrate, is used chiefly in reference to domestic animals, especially the horse, and caponize, also meaning to castrate, most commonly has reference to the male domestic fowl, but both are sometimes used contemptuously of human beings.