Q. I keep hearing the word nauseous (causing sickness) used as if it meant nauseated (feeling sick). That’s wrong, isn’t it? Tim/Old Mission Peninsula, MI
A. Your observation is correct. Both words come from the Greek word naus, meaning a ship, so the original nausea was caused by the action of waves.
These days, nauseated means “suffering from nausea,” while nauseous means “causing nausea.” That means that if you misuse the terms and say “I’m feeling nauseous,” a number of unkind people will agree with you.
But it’s strange how words get turned around. Originally (1613), nauseous meant “inclined to sickness or nausea.” In turn, nauseated originally meant “causing nausea” (1659). So the words have undergone a complete transformation, and the mistake that you point out is really a return to how things once were, however unwitting the restoration may be.
It’s another good illustration of how ephemeral word usage and grammar conventions actually are.
(substitute @ for AT above)