Definition of: gnomon

(nō′mon) noun
1. The triangular piece whose shadow points out the time of day on a sundial, or anything, as a pillar, used for a similar purpose.
2. The index of the hour circle of a globe.
3. Geom. The figure that remains after a parallelogram has been removed from the corner of a similar but larger parallelogram, as BCIGDE or FCAGHE. The diagonally opposite parallelograms ADEB, EHIF, or GHED, EFCB, are called complements of each other or of the whole parallelogram.
4. Math. One of the terms of an arithmetical series by which polygonal numbers are found: also gnomonic number. [<Gk. gnōmōn an indicator <gnō-, stem of gignōskein know]
GNOMON