“Gruel,” which you often read about in old stories about unfortunate waifs in nineteenth-century orphanages, turns out to be a catchall term for various kinds of broth. It could be anything from boiled oatmeal to thin soup. It was served in orphanages, and also to people suffering from various illnesses. But “gruel” is a light, thin liquid, easy to prepare and easily digested. So why, in that case, does “grueling” mean something physically exhausting?
It all started in the 1300s, which is when the word “gruel” appeared in English. Like any number of interesting foods, it came from France, where it simply meant “ground-up grain.” However it may have been regarded in France, English cooking soon made sure that while gruel was widely available and very helpful to anybody who had an upset stomach, it wasn’t anybody’s favorite. The word came to have a figurative sense as well, and those figurative meanings were nearly as flexible as the various recipes for making the stuff. One way “gruel” was used was to mean something that “lacks substance.” Another was as anything unpleasant, as in having to take your (nasty) medicine. In the 1700s, being “given one’s gruel” also meant getting punished, even getting killed. That produced the verb version of the word, where “to gruel” meant to punish. From there, in the early 1800s, “to gruel” came to mean “to exhaust or disable”. A few decades after that, something physically exhausting (or “punishing”) started to be called “grueling”.
Nowadays “gruel” has lost its figurative meanings, as well as pretty much any meaning other than broth, when it’s used at all. But “grueling” still refers to an epic physical struggle.
After a particularly grueling task, anybody might find themselves in a hebetudinous state. “Hebetude” is a rare word, possibly because it has just about the same meaning as other words everybody does know — maybe most people just feel too dull or lethargic to trot out “hebetude” instead of, well, “dull” or “lethargic.” “Hebetude” comes from the Latin root “hebes,” which means dull (as in a knife blade) or blunt. There was also a Greek goddess “Hebe,” but she seems not to have any connection to this word. The Romans used “hebes” to refer to blades, and also to refer to people. They didn’t mean lazy or tired, though; they meant stupid.
“Hebetude” in English was as popular as it ever got (which is “not very”) in the 1800s. While it was sometimes used in the Roman sense to impugn someone’s mental sharpness (see what I was saying? With “sharp” and “dull”, who really needs “hebetude”?), it’s generally meant something more like lethargy or apathy. The novelist Joseph Conrad used “hebetude” several times in his books, including this passage from Nostromo: “From that solitude, full of despair and terror, he was torn out brutally, with kicks and blows, passive, sunk in hebetude”. And even though it’s rare, “hebetude” is still occasionally used, as in this 2001 column from The Washington Post: “Too many Americans slouch toward a terminal funk of hebetude and sloth.” That article should have gone on toe explain that we’re sliding into hebetude only because anything else just seems like it would be too grueling.