kurioza

The clearest false friend in the whole Esperanto core vocabulary, and the reason it is worth learning carefully is that the wrong reading produces a sentence that is grammatical, fluent and about something else entirely.

Kurioza describes the thing, never the person. It means odd, quaint, peculiar, worth a second look - the sense English keeps in "a curious little shop" or "a curio". It does not mean eager to know. If you want that, the word is scivola, literally "wanting to know", from scii plus voli, or scivolema for someone who is habitually nosy. So:

• kurioza knabo - a peculiar boy, an odd fish
• scivola knabo - an inquisitive boy, one who asks questions

Say the first when you mean the second and you have just called a child strange to their face. It is a small mistake with a large blast radius, and English speakers make it constantly because "curious" in English does both jobs and lets context sort it out.

Kurioza is also the cornerstone example in false friends in Esperanto, where the rest of the family lives: aktuala (current, not actual), eventuala (possible, not eventual), parenco (relative, not parent), sensa (of the senses, not senseless). Esperanto is an easy language with a hard corner, and this is it - the words that look borrowed from your own language and are borrowed from somebody else's.

Against stranga, which is plain strange and can be unsettling, kurioza is warmer: it carries a note of the interesting, the collectable, the thing you would point out to a friend.