triplicity n (astrology) one of four groups of the zodiac where each group consists of three signs separated from each other by 120 degrees n the property of being triple Usage(s) Tobey, of course, discovers Quigley's triplicity and decides to punish him with overindulgence. For Jones, this triplicity of Whites before him has taken on a weird, nightmarish character. Gabrielle's duplicity soon turns into triplicity, and before the episode ends, she has two more victims. Synonym(s) trigon