Orchidectomy
The excision of one or both of the testicles; castration.
This is derived from the Greek ὄρχις (orkhis, a testicle) + ἐκτοµή (ektomi, cutting-out).
According to the OED the first recorded usage was in 1870.

And just to remove any confusion, the group of plants called orchids are so named because of the testicular appearance of the roots of some species.