Definition of gnomon
1 : an object that by the position or length of its shadow serves as an indicator especially of the hour of the day: such asa : the pin of a sundialb : a column or shaft erected perpendicular to the horizon
2 : the remainder of a parallelogram after the removal of a similar parallelogram containing one of its corners
From the M-W Editors
Illustration of gnomon
Origin and Etymology of gnomon
Latin, from Greek gnōmōn interpreter, pointer on a sundial, from gignōskein
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