prime meridian: meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England)
meridian: an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator
angiospermae: comprising flowering plants that produce seeds enclosed in an ovary; in some systems considered a class (Angiospermae) and in others a division (Magnoliophyta or Anthophyta)