Euphemisms substitute a mild or vague expression for one that is considered to be offensive or harsh. They often come into play with words concerned with religion, sex, death, and excreta. For example, if you wanted to employ a euphemism to say that someone died, you might say that he passed away or departed.
The derivation of euphemism is the Greek root eu-, which means “good,” and pheme, which means “speaking.” During religious ceremonies, ancient Greeks superstitiously avoided euphemes. These were words or phrases that were considered sacred, such as the name of a deity like Persephone.
Ancient Greeks weren’t the only people to consider certain words ineffable. Religious Jews use the tetragrammaton or, tetragram, as a sort of euphemistic Hebrew name for God that was supposedly revealed to Moses on Mount Sinai. It consists of the four consonants Y H V H or Y H W H. It’s modern transliteration is Jehovah or Yahweh.
Blaspheme is the opposite of eupheme. What’s the difference between blasphemous language, cursing, and swearing? Read about that here.