Pardon me, but when a polite term is substituted for a blunt, offensive one, you should call it a euphemism.
Euphemism is from Greek euphemismos, meaning "good speech," and it's a way that we paper over uncomfortable things with more pleasant-sounding words. These days we tend to use euphemisms when talking about anything having to do with elimination of bodily waste: toilet, bathroom, and water closet were all originally euphemisms. The military is also notorious for using euphemisms, like saying "neutralizing the target" instead of "killing someone."
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