taboo deformation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The alteration of a tabooed word to make a socially acceptable word, as by the replacement of one or more sounds in the tabooed word or by the substitution of a similar-sounding word for one or more words in a compound.
• noun A word formed by such alteration, such as darn from damn or dadburned from goddamned.