Indirection

I got up around 2:45 to have a slash (as the Brits say) or void my bladder (as the prim say), which is more or less invariable with me, since I can count on one hand the number of times I've slept through the night in living memory, and after I'd gotten back into bed I thought how nice it was to be horizontal, which of course made me think about the word "horizontal", obviously descended from "horizon", which is probably Latin through Greek, and its opposite, "vertical", which is just as obviously derived from "vertex" and which must be Latin, and by that time I was wide awake, so I decided to get up and do the research (and also check on the word "diagonal", which was I was guessing was Greek), after which, I hoped, I'd be able to get some sleep.

"Horizon" comes from Greek "horizein", "to limit or bound", and thence to the noun "horizon", "a circle which bounds"; though we think of the horizon as a line, it can also be seen as a circle which encompasses all we can see. We say "horizontal" rather than the plausible "horizonal" because "horizont-" is the Latin combining form.

"Vertical" is straight from Latin "verticalis", which does in fact come from "vertex", "the crown of the head" (which it still means in anatomy), from the verb "vertere", "to turn", also seen in such words as "vertigo" (the world whirling around you), "vertebra" (the spine as the central axis of the body), and "versus" ("turned against").

"Diagonal" (which irresistibly calls to mind J.K. Rowling's clever Diagon Alley), describes the edge of a right triangle which is neither horizontal nor vertical, and is composed of "dia-", "across", plus "-gon", "angle", therefore literally "from angle to angle".

And now can I get back to bed? Not likely.