Quadragesima |
the first Sunday of Lent. |

quadrangle |
a closed two-dimensional figure with four sides, such as a rectangle or parallelogram. [3 definitions] |

quadrant |
one quarter of the arc of a circle. [5 definitions] |

quadraphonic |
of, concerning, or used for the reproduction of sound, esp. music, over four distinct channels. |

quadrat |
see quad^{2}. [2 definitions] |

quadrate |
a square or rectangle. [5 definitions] |

quadratic |
of, concerning, or involving mathematical expressions containing a variable that is raised to the second power at most. [2 definitions] |

quadratic equation |
in algebra, an equation in which the square is the highest power to which the unknown quantity is raised. |

quadrature |
the act or process of squaring. [3 definitions] |

quadrennial |
happening once every four years. [3 definitions] |

quadri- |
four. |

quadriceps |
a group of four large muscles located at the front of the thigh. |

quadrilateral |
having four sides. [2 definitions] |

quadrille^{1} |
a formal square dance with five separate movements executed by four couples. [2 definitions] |

quadrille^{2} |
an eighteenth-century card game for four players. |

quadrillion |
the number represented by the Arabic numeral 10^{15}. [2 definitions] |

quadripartite |
having four parts or divisions. [2 definitions] |

quadriplegia |
paralysis of the entire body, from the neck down. |

quadrivalent |
having a valence of four; tetravalent. [2 definitions] |

quadrivium |
in medieval universities, the higher section of the liberal arts, comprising arithmetic, geometry, astronomy, and music. (Cf. trivium.) |

quadroon |
a person who is one quarter black and three quarters white; the child of a mulatto and a white person. |