gnomon

gnomon (NOH-mon) - n., the part of a sundial that casts a shadow used to tell the time.


There are a few other senses, including an object that casts a shadow for the purpose of determining latitude, but they are minor and/or obsolete so I'm ignoring them. The most recognizable form is a slanted edge such as this:


Thanks, WikiMedia!

but they come in many other shapes, including rods (either vertical or slanted) and a bead on a wire. The mathematics of constructing a sundial is fun, actually, but I don't have enough space in this margin to talk about it at length. The name comes from Latin gnōmōn, same meaning, borrowed from Greek gnṓmōn, same meaning, but originally interpreter/knower, from gignōskein, to know.


(Sorry for the unexpected absence -- a round of Covid. Back now, though.)

---L.