Etymology
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gnomon (n.)

"vertical shaft that tells time by the shadow it casts" (especially the triangular plate on a sundial), 1540s, from Latin gnomon, from Greek gnōmōn "indicator (of a sundial), carpenter's rule," also, in plural, "the teeth that mark the age of a horse or mule," literally "one that discerns or examines, interpreter, expert," from gignōskein "to come to know," from PIE root *gno- "to know." In geometry from 1560s, from a use in Greek. In early use in English sometimes folk-etymologized as knowman. Related: Gnomonic.

updated on July 09, 2019

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Definitions of gnomon from WordNet

gnomon (n.)
indicator provided by the stationary arm whose shadow indicates the time on the sundial;
Etymologies are not definitions. From wordnet.princeton.edu, not affiliated with etymonline.