What are some synonyms for 'euphemism'?

paranym, which is defined as

a word or words whose meaning is altered to conceal; an evasion; see euphemism (by Wordnik)

and

euphemism; word whose meaning altered to conceal evasion (by Phrontistery)

General synonyms could be circumlocution, substitute or alternative. If you want to give the impression that the replacement term is nicer than the original, you can use polite term, understatement, genteelism (my personal favorite). If you're going the other way, i.e. using a more unpleasant alternative, that would be a dysphemism (exact antonym of euphemism). Though I can't think of any simple synonym of dysphemism, you could be talking about the slang term for X, the harsher term for, the rude term for…

• circumlocution
• bowdlerism
• code word
• allusion

The best way to classify words along the lines you are considering is by connotation vs. denotation. For example, English provides a number of words for 'an olfactory experience': scent, fragrance, odor, perfume, smell, aroma, stench, etc. Ranking these words from positive to negative forms a continuum of synonyms.