A eunuch is a castrated human male. The castration can be only of the testes, or also include the penis, known as a penectomy (often with a tube inserted to keep the urethra open, called a urethral rerouting). The practice was established before 700 BC and accounts of eunuchs are known throughout history.
The English word eunuch is from the Greek eune ("bed") and ekhein ("to keep"), effectively "bed keeper." This indicates the traditional role of the eunuch—as a reliable keeper of a ruler's harem. Other servants or slaves were also castrated in order to make them 'safer,' either in childhood or later.