■ noun a celestial body moving in an elliptical orbit round a star.
↘( the ~ ) the earth.
↘ chiefly Astrology & historical a celestial body distinguished from the fixed stars by having an apparent motion of its own (including the moon and sun).
Phrases
what ~ are you on? Brit. informal used to indicate that someone is out of touch with reality.
Derivatives
~ary adjective
~ologist noun
~ology noun
Origin
ME: from OFr. ~e , from late L. ~a , ~es , from Gk planētēs 'wanderer, ~', from planan 'wander'.