Learn English – Are there by chance any synonyms for “synonym”

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)

Contemptible behavior or base behavior convey contempt without vulgarity. But I think it will be impossible to quite satisfy your requirement for a word with “about the same impact”. I doubt that vulgarity can be matched for impact by anything but blasphemy – and that only when your audience is religious.