Keen means sharp or intense, whether describing a physical edge, a mind, or a feeling.

A knife with a keen blade cuts cleanly through rope or vegetables. Similarly, a person with a keen mind thinks clearly and quickly, noticing details others miss. Sherlock Holmes had a keen sense of observation: he spotted clues that everyone else walked right past.

The word also describes strong enthusiasm or interest. If you're keen on soccer, you love playing it and never miss a chance to practice. A student keen to learn asks thoughtful questions and digs deeper into subjects that fascinate them. When your friend suggests going to the science museum and you reply, “I'm keen!”, you're expressing genuine excitement about the idea.

You might have keen eyesight that lets you read distant signs, a keen sense of smell that notices when cookies are baking three rooms away, or keen hearing that picks up whispered conversations. Animals like hawks have famously keen vision for spotting prey from high in the sky.

The opposite of keen is dull: a dull blade that can't cut, a dull mind that misses obvious things, or feeling dull about an activity that doesn't interest you at all.