planet（プラネット）
要点惑星
意味
- 惑星,遊星
例文
Neptune is the eighth planet of the solar system.
海王星は太陽系の8番目の惑星だ。
What's the difference between a star and a planet?
星と惑星の違いは何ですか？
Jupiter is the biggest planet in our solar system.
木星は太陽系で最も大きな惑星です。
語源
ギリシャ語planetes「さまよう者」から。星座の中をさまようように動いて見える星「惑星」。
英語の原文（Wiktionary）
From Middle English planete, from Old French planete, from Latin planeta, planetes, from Ancient Greek πλανήτης (planḗtēs, “wanderer”) (itself an ellipsis of ἀστέρες πλανῆται (astéres planêtai, “wandering stars”)), from Ancient Greek πλανάω (planáō, “wander about, stray”), of unknown origin. Cognate with Latin pālor (“wander about, stray”), Old Norse flana (“to rush about”), and Norwegian flanta (“to wander about”). More at flaunt. So called because they have apparent motion, unlike the "fixed" stars. Originally including also the moon and sun but not the Earth; modern scientific sense of "world that orbits a star" is from 1630s in English.