If people have keen eyes or ears, or keen minds or intellects, then those things, too, are "sharp" in the sense that they're strong and powerful. I bet you're a keen reader: a sharp, smart reader who sees and notices all kinds of hints and details that other readers gloss right over. Like a keen knife that slices through a strawberry, your keen mind cuts straight through your book.
That's because "keen" also means "interested, eager, excited, and curious." We often describe people's interest as keen, or their curiosity as keen. When you take a keen interest in something, you take a strong, sharp, intense interest in it. And when your curiosity about something is keen, it's very strong. This kid is peering into the terrarium with keen interest.
We often say that people are keen on something, or keen to do something, meaning they're really interested in it, they love it, or they're excited and eager to do it or to learn about it. Here's Mr. Bean, looking very keen to do, well, whatever! He's excited and ready to go.
And here's Sam, who's keen to cook and eat some potatoes. He's really tired and hungry, and can't wait to dig into a delicious meal. And he's particularly keen on potatoes.
One last thing to know! The word "keen" has a homograph, which means that there's another word, "keen," with the same spelling but a totally different history and meaning. To keen is to cry or wail loudly because you're very sad. Here's a keening puppy. Maybe he feels lonely, or scared, or hungry. I bet you'd pick him right up and snuggle him if you heard him keening.
Remember: keen things are strong or sharp, and keen people are eager and excited.
Idea 1: "Ever since I was (a certain age), I've had a keen interest in (some game, sport, activity, musical instrument, or other topic); I've always hoped to (accomplish something specific in this area)."
Idea 2: "I really (loved or hated) (doing something); that's why I'm (so keen, or not so keen) on doing it again soon."
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