Moon  —n. 1 a natural satellite of the earth, orbiting it monthly, illuminated by the sun and reflecting some light to the earth. B this regarded in terms of its waxing and waning in a particular month (new moon). C the moon when visible (there is no moon tonight). 2 satellite of any planet. 3 (prec. By the) colloq. Something desirable but unattainable (promised me the moon). —v. 1 wander about aimlessly or listlessly. 2 slang expose one's buttocks.  many moons ago a long time ago. Moon over act dreamily thinking about (a loved one). Over the moon colloq. Extremely happy.  moonless adj. [old english]