Kings in the ancient world often used castrated men to work in their royal harems. In time, the word came to refer to royal officials in general, whether or not they were castrated. Israel’s law prohibited physical eunuchs from being part of the faith community.
The most interesting Bible reference to physical eunuchs is the statement of Jesus that some were eunuchs because they were born that way, others were made that way by men, and others made themselves eunuchs because of the kingdom of heaven.
“He who is able to accept it, let him accept it” (Matt. 19:11–12). His meaning seems to be that some people (like Jesus Himself ) can live a celibate life, particularly if they have a spiritual motivation.
He did not mean that a man should castrate himself, though some have interpreted it that way.
See 457 (the Ethiopian eunuch).