When something seems fishy, it feels suspicious or questionable, like something's not quite right even if you can't prove it yet. If your friend suddenly has a completely different excuse for missing your birthday party than the one they told you yesterday, that's fishy. When a deal seems too good to be true, like someone offering to sell you a brand new bicycle for five dollars, your instincts tell you something's fishy about it.

When you sense something fishy, you're picking up on small clues that don't add up, like pieces of a puzzle that don't quite fit together. Maybe someone's story has holes in it, or their behavior suddenly changed for no clear reason.

Notice that calling something fishy doesn't mean you know exactly what's wrong. It's that gut feeling that makes you want to investigate further or be more careful. A scientist might find fishy data in an experiment that doesn't match previous results. A detective investigating a case looks for details that seem fishy.