The word nauseated means to be affected with nausea or to feel sick to your stomach. Nauseous describes something that causes a feeling of nausea. These words have the same root word, nausea, a Latin word that refers specifically to seasickness. Nauseous and nauseated originally had different definitions. In current common usage, though, the words have evolved to become practically interchangeable.
The word nauseous describes something that causes a feeling of nausea or disgust. Here’s an example: “The nauseous odor made the boy feel sick.” In this sentence, the word nauseous modifies the noun odor, and it explains that the odor was sickening.
Many people consider this the only correct way to use the word nauseous. However, in everyday speech, the word often means the actual feeling of nausea. To illustrate, look at this example: “The odor made the boy feel nauseous.” In this sense, the adjective nauseous modifies the boy, but it doesn’t mean that the boy himself is sickening or revolting. It simply means that the boy is feeling sick to his stomach.
Nauseated means to become affected with nausea. This is the traditional way to use the word nauseated. For example, if you were feeling sick to your stomach, you would say, “I’m feeling nauseated,” rather than “I’m feeling nauseous.” However, as explained above, this distinction has faded over time.
Nauseated also means to create a feeling of nausea, as in “The experience nauseated him.” In this sense, nauseated is used to explain what the experience did to him: It made him feel sick.
Strict grammarians may claim that nauseous describes something that creates a feeling of sickness or revulsion, and that nauseated means to feel ill. However, common usage actually reverses these two meanings, and the reversal has become so popular that many dictionaries now carry both meanings for both of these words, making them virtually interchangeable.