hum

The root hum goes all the way back to a Proto-Indo-European root dʰǵʰem- meaning simply 'earth, the ground.' In Latin this surfaced as humus — the soil under your feet — and almost everything in this family is a variation on the idea of being low, of the earth, brought down to the ground.

Start with the most literal sense. humble comes from Latin humilis, 'low, on the ground.' A humble person keeps themselves low, doesn't tower over others — and that physical lowness became the moral virtue of modesty. humility is the noun for that quality, and to humiliate someone is literally to push them down to the ground — to lower them in front of others. humbly is just the adverb. Picture the whole cluster as a person bowing low, face toward the earth.

Now take the lowness underground. ex- (out) + humus gives exhume: to dig a buried body out of the earth — and figuratively to bring a hidden, buried thing back to light. Its opposite, inhume, is to put a body into the earth (bury it); exhumation is the digging-up. And posthumous looks like it belongs here — 'after the earth/burial' — but is actually a folk-etymology twist: Latin postumus meant simply 'last, last-born,' and scribes who connected it to humus added the -h-, fixing the modern sense 'happening after someone is in the ground': a posthumous award, a posthumous novel.

The biggest surprise is human itself. Latin homo (a human being) and humus (earth) come from the very same ancient root: a homo was literally an earthling, an 'earthly being' — as opposed to the gods above. So human, humane (kind, behaving as a good human should), humanity, humankind, humanitarian, humanism and all the human- compounds trace back to the same dirt. When you say someone is only human, you are unknowingly calling them a creature of the earth. (Note: homicide sits here too — homo 'human' + cide 'killing' — but its second half belongs to the [cid] family.)

Finally, a near-identical-looking branch from Latin humēre, 'to be moist.' This gives the transparent humid, humidity, humidify, humidifier — all about water in the air. The fun jump is humor: medieval medicine believed the body held four humors (fluids — blood, phlegm, two biles), and the balance of these moistures determined your temperament. 'In a good humor' originally meant your fluids were well-balanced. Over centuries the fluid meaning faded and 'humor' came to mean mood, and then specifically the funny, amusing kind of mood — giving humorous, humorist, humorless, and the compounds good-humored / ill-humored. So the next funny joke you hear is, etymologically, a well-balanced bodily fluid.