To be dubious means to feel doubtful or uncertain about something. When you're dubious about whether your team will win the championship, you have serious questions about it happening. When a friend makes a dubious claim like “I can hold my breath for ten minutes,” you don't quite believe them.

The word often suggests more than simple uncertainty. It carries a hint of suspicion or skepticism. If your sister offers you a “delicious” sandwich that looks questionable, you might give it a dubious look, one eyebrow raised, wondering what's really in there. A dubious excuse is one that sounds made up. A dubious plan is one that seems unlikely to work.

Something dubious can also be morally questionable. A student using dubious methods to win the science fair might be bending the rules in ways that don't seem quite right, even if they're not outright cheating. A business deal might be legally allowed but still dubious if it takes advantage of people.

The related word dubiously describes doing something while feeling doubtful: “She dubiously agreed to try the mysterious cafeteria food.” When you feel dubious, you're reserving judgment because something doesn't quite add up.