gnomon

UK: /ˈnəʊmɒn/ US: (nō′mon)

WordReference Random House Unabridged Dictionary of American English © 2026

gno•mon  (nō′mon), n. 

1. Time the raised part of a sundial that casts the shadow;
   a style. See illus. under sundial. 
2. Astronomy an early astronomical instrument consisting of a vertical shaft, column, or the like, for determining the altitude of the sun or the latitude of a position by measuring the length of its shadow cast at noon.
3. Mathematics [Geom.] (formerly) the part of a parallelogram that remains after a similar parallelogram has been taken away from one of its corners.

• Greek gnó̄mōn literally, interpreter, discerner
• Latin gnōmōn pin of a sundial
• 1540–50

Collins Concise English Dictionary © HarperCollins Publishers::

gnomon / ˈnəʊmɒn/ noun

1. the stationary arm that projects the shadow on a sundial
2. a geometric figure remaining after a parallelogram has been removed from one corner of a larger parallelogram

Etymology: 16th Century: from Latin, from Greek: interpreter, from gignōskein to know

gnoˈmonic, gnoˈmonical adjective