gnomon

The story

1. Proto-Indo-European · derived from*ǵneh₃-“to know”
2. Ancient Greek · derived fromγνώμων“discerner, interpreter; carpenter’s square; gnomon of a sundial; (geometry) gnomon”
3. Latin · borrowed fromgnōmōn
4. French · borrowed fromgnomon
5. English todaygnomon

Borrowed from French gnomon, or directly from its etymon Latin gnōmōn, or directly from its etymon Ancient Greek γνώμων (gnṓmōn, “discerner, interpreter; carpenter’s square; gnomon of a sundial; (geometry) gnomon”), from γιγνώσκω (gignṓskō, “to be aware of; to perceive; to know”), ultimately from Proto-Indo-European *ǵneh₃- (“to know”); the word is thus related to know. The geometry sense (sense 4) is from the resemblance of the plane figure to a carpenter’s square. Similarly, a gnomon in mathematics (sense 5) is also shaped like a carpenter’s square when depicted pictorially if the figurate numbers are squares.

Words from the same roots

First known use, by meaning

• from mid 16th c. An object such as a pillar or a rod that is used to tell time by the shadow it casts when the sun shines on it, especially the pointer on a sundial.