What do we call a more polite word to express something unpleasant? (example: to say "let go" instead of "you're fired")

Read the passage. and thus they fought all the long day, and never stinted till the noble knights were laid to the cold earth. and ever they fought still till it was near night, and by then was there a hundred thousand laid dead upon the down. in the passage from morte d’arthur by sir thomas malory, what are the bolded words an example of?