from The Century Dictionary and Cyclopedia

  • n. On a sun-dial, the triangular projecting piece which by its shadow shows the hour of the day; also, any index to a sun-dial or to a meridian-mark, especially a very large one. The early gnomons used for astronomical purposes were vertical pillars or obelisks.
  • n. The index of the hour-circle of a globe.
  • n. A piece of a parallelogram left after a similar parallelogram has been removed from a corner of it. Thus, in the figure, EFGBCD is a gnomon.
  • n. An odd number; one of the terms of an arithmetical series by which polygonal numbers are found. Also called gnomonic number.



'Gnomon' comes from the Greek 'gignoskein,' to know.