Is it a eunuch or An eunuch?

Answer 1

According to the American Heritage Dictionary of the English Language, this is the definition of a eunuch:

1. A castrated man employed as a harem attendant or as a functionary in certain Asian courts.
2. A man or boy whose testes are nonfunctioning or have been removed.
3. Informal. An ineffectual, powerless, or unmasculine man.

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Eunich is a castrated attendant in a harem. The word is also used with reference to a man whose testicles don't function (or have been removed).

Answer 2

A eunuch is commonly used.