early 14c., from Old French constellacion "constellation, conjuncture (of planets)," from Late Latin constellationem (nominative constellatio) "set with stars," from constellatus, from Latin com- "with" (see com-) + past participle of stellare "to shine," from stella "star" (see star). Originally in astrology, of position of planets ("stars") in regard to one another on a given day, usually one's birth day, as a determination of one's character. "I folwed ay myn inclinacioun/By vertu of my constillacioun" (Chaucer, "Wife's Prologue," c.1386). Modern astronomical sense is from 1550s.