Unclean means dirty, impure, or contaminated with something that makes it unsafe or unsuitable to use. An unclean kitchen counter covered with crumbs and spills needs to be wiped down before you make a sandwich. Unclean water might contain bacteria that could make you sick if you drink it.

The word goes beyond just physical dirt. In many religious traditions, unclean describes things considered spiritually impure or forbidden. Ancient Jewish dietary laws, for example, labeled certain animals as unclean and therefore not to be eaten. These rules weren't about hygiene but about religious practice and identity.

You might say a room feels unclean when it's messy and grimy, or describe an unclean conscience when someone feels guilty about something they've done wrong. A restaurant with an unclean kitchen risks making customers sick and will likely be shut down by health inspectors.

The opposite of unclean is clean, obviously, but also pure, sanitary, or hygienic. When doctors sterilize their instruments, they're making sure everything is perfectly clean, with no contamination that could harm patients. Unclean suggests something needs attention before it's safe or acceptable to use.