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planet

n.
US //ˈpɫænət// UK //plˈænɪt// plan·et
  1. 1 the Earth (n.)
    B1 Intermediate

    the world we live on, especially when talking about the environment.

    the Earth, often used in environmental or global contexts to emphasise its uniqueness or fragility.

    Example

    We must work together to protect the planet for future generations.

    Example

    The summit focused on how international policy can mitigate the damage humans have caused to the planet over the last century.

    Usage

    Almost always used with the definite article 'the' or the demonstrative 'this'.
  2. 2 historical/astrological body (n.)
    C2 Proficiency Archaic Technical

    in the past, any object in the sky that moved differently from the stars, including the sun and moon.

    historically, any of the seven celestial bodies visible to the naked eye that moved against the background of fixed stars.

    Example

    Ancient observers noticed that certain planets moved across the sky while stars stayed in place.

    Example

    In medieval cosmology, the Sun and Moon were classified as planets alongside Mercury, Venus, Mars, Jupiter, and Saturn.

    Teacher's tip

    This sense is mostly found in historical texts or discussions of astrology; modern science excludes the Sun and Moon from this category.
    • wandering star
Origin

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. The Greek word is an enlarged form of πλάνης (plánēs, “who wanders around, wanderer”), also "wandering star, planet", in medicine "unstable temperature."

Word family

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