Inadvertent means accidental or unintentional. When something is inadvertent, it happens without planning or even awareness. You might make an inadvertent mistake on your homework when your mind wanders and you write the wrong answer, even though you knew the right one. A friend might give away the ending of a movie through an inadvertent comment, not realizing you hadn't seen it yet.

The word often appears when explaining that no harm was meant. A teacher might say, “Your inadvertent interruption during the presentation wasn't a big deal,” meaning you didn't mean to disrupt things. Scientists worry about the inadvertent effects of new technologies: consequences they didn't predict or intend.

Inadvertent differs from careless. Carelessness suggests you should have paid more attention, while inadvertent actions can happen even when you're trying your best. If you inadvertently step on someone's toe in a crowded hallway, you simply didn't see their foot.