A serious infectious disease, caused by bacteria, that spreads mainly through sexual contact; a pregnant woman can also pass it to her baby. It moves in stages — first a painless sore that heals on its own, then a rash and flu-like illness, then often years of nothing at all — and that quiet middle stage is what makes it dangerous, because someone can feel perfectly well while the infection is still there. Left untreated for many years it can damage the heart, the brain and the nerves. Before penicillin it was a genuine terror of European life and killed or maddened a long list of famous people; today it is cured with antibiotics, though case numbers have been rising again in many countries, Taiwan included, which is why it still appears in health campaigns rather than only in history books. In English it is a plain medical noun, uncountable, and takes a singular verb ('syphilis is curable'). Be aware that it still carries heavy shame in ordinary talk, so outside a clinic people use it as an insult or avoid saying it at all — the general polite phrase is 'a sexually transmitted infection' or 'an STI'. The stress falls on the first syllable: SIF-uh-lis.