once in a blue moon

: one time and no more

: at any one time : under any circumstances : ever

: at some indefinite time in the past : formerly

: one single time : one time at least

: that once was : former

: at the moment when : as soon as

: of the color whose hue is that of the clear sky : of the color blue (see ²blue 1)

: bluish

: discolored by or as if by bruising

: a color whose hue is that of the clear sky or that of the portion of the color spectrum lying between green and violet

: a pigment or dye that colors blue

: bluing

: to make blue (see ¹blue)

: to turn blue

: the earth's natural satellite (see satellite 2a) that shines by the sun's reflected light, revolves about the earth from west to east in about 29¹/₂ days with reference to the sun or about 27¹/₃ days with reference to the stars, and has a diameter of 2160 miles (3475 kilometers), a mean distance from the earth of about 238,900 miles (384,400 kilometers), and a mass about one eightieth that of the earth

: one complete moon cycle consisting of four phases (see ¹phase 1)

: satellite

: to spend in idle reverie : dream

: to expose one's naked buttocks to

: to spend time in idle reverie : behave abstractedly