Second to last sentence, near the bottom of the page. Writing "an euphemism" is incorrect.
"The form an is used before words that begin with a vowel sound (even if spelled with an initial consonant, as in an hour), and a before words that begin with a consonant sound (even if spelled with a vowel, as in a European)." What's important is how the word
sounds, not how it's spelled.
The word "euphemism" starts with a consonant y-sound, so "a euphemism" is correct.
I point this out and correct it only because I know a lot of people with English as a second language read stuff on this site, so I don't want them to get the wrong idea about how to use the indefinite article. But for that matter, many native English speakers often make this mistake too, now that I think about it.