gnomon

The word 'gnomon' entered English in the mid-16th century directly from Latin 'gnomon', which itself was borrowed from the Greek 'gnōmōn', meaning "one who knows or examines," an "indicator." Its Greek root is tied to the verb 'gignōskein', "to know," which traces back to the Proto-Indo-European root ǵneh₃-, meaning "to know." The semantic logic is beautifully direct: the object that "knows" or "indicates" the time. Originally used for the pointer on a sundial, its geometric sense arose from Euclid's use of the term for a similar figure-shaping concept, preserving the core idea of a defining or measuring element.

The word is a simplex loanword from Greek. It is not productively segmented in modern English spelling. The Greek root is 'gnōmōn' (γνώμων), meaning "indicator," "interpreter," or "carpenter's square," from the verb 'gignōskein' (γιγνώσκειν), meaning "to know."