noun

• (astronomy, dated) An asteroid of any size
  "The group of small bodies that circle round the Sun, outside the orbit of Mars, are known under the designation of the planetoids."
• (astronomy, dated) An asteroid-like body in an orbit beyond the asteroid belt, such as a centaur or Kuiper belt object
• (astronomy) A larger, planetary, body in orbit around the Sun, such as Vesta or (candidate) dwarf planets such Eris or Sedna
  "After discovering "planetoids", bodies orbiting the Sun, even larger than Pluto's moon Charon ... the question of how Sedna and other planetoids came to be."
• (astronomy) Any planetary body, including classical planets and moons: a planetary-mass object
  "Plate tectonics is a style of convection for an active planetoid where lid fragment (plate) motions reflect sinking of dense lithosphere in subduction zones […] In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects, which we informally call “planetoids”."