Definition -
(1) Substituting the normally-used word with a word that you believe is politer or classier.
(2) A word of this type.

Example -
Saying tummy instead of stomach because you feel that the latter is too harsh.

Oxford English Dictionary -
The term's first citation in this sense is from 1926:
"By genteelism is here to be understood the substituting, for the ordinary natural word that first suggests itself to the mind, of a synonym that is thought to be less soiled by the lips of the common herd, less familiar, less plebeian, less vulgar, less improper."
(Fowler Mod. Eng. Usage 212/2)

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