Where to start with this word? I’m not sure I’ll be able to cover everything…
Well, I can’t remember what my first encounter with it was – whether it was in reference to a transit vehicle or in the phrase sol lucet omnibus. I know I learned the Latin phrase (for some reason) when my age was still in the single digits, and I knew it meant “the sun shines everywhere,” though I didn’t actually grasp the figurative value of it, and of course I said it in like English.
I naturally knew the word bus for the vehicle before I knew the word omnibus (which I might have first seen in a Richard Scarry book), and so I inferred not unreasonably that an omnibus might be some special kind of bus – perhaps one of those red double-decker ones I saw in Scarry’s cartoons. It does have a sound of some greater quality. Once I had learned that it was really just the same vehicle, I concluded that it was a fancier, more British way of saying the thing, like motorcar or automobile. And indeed it does have a higher, more archaic (even quaint) tone, and I would say sounds more British to North American ears.
How did this word come about, anyway? Was the omni grandiosely tacked on to the humble bus? Well, no, of course it went the other way: just as automobile became auto (now itself a rather dated-sounding word), omnibus became bus. Actually, a closer analogue would be trimming helicopter to copter. You see, the roots in automobile are indeed auto and mobile, while the roots in helicopter are helico and pter – and as to omnibus, it’s actually the noun root omn(i) with the inflectional ending ibus (as in pax in hominibus, “peace among people”). It means “for all” – it’s the dative plural of omnis.
And what that means is that it’s not a masculine singular, and so it doesn’t pluralize to omnibi. This puts it in the same set as mumpsimus (which comes from an inflected verb), vade mecum (in which mecum is a compound meaning “with me”, so it doesn’t pluralize as meca), and arguably octopus (which is a Latinization of a Greek word wherein the source of pus is pous, meaning “foot”). Although, as Ross Ewage lately tweeted, “If the plural of omnibus were omni-bi, they would take everyone,” it’s not and they don’t. Well, not in the sense he undoubtedly meant, anyway.
They do, of course, take all comers when they’re part of a transit system. And, tangentially, if you ride a bus often, you will likely see people reading from an omnibus every so often. By which I mean the book they are reading is an omnibus edition – not an edition made for reading on the bus, but a volume of collected works by an author. (This is a more British term, generally.) For instance, on my shelf I have The First Rumpole Omnibus, by John Mortimer, which is the first anthology of tales of Rumpole of the Bailey.
I think it quite possible that Mortimer (or whoever named the book) also liked the added legal overtone of omnibus. You see, another common use of omnibus is in omnibus bill, which is not the name of a bus driver or anthology editor but rather a bill submitted to legislative approval that is a collection of unrelated pieces (what Kurt Vonnegut, among others, has termed a blivet: ten pounds of shit in a five-pound sack).
By the way, omnibus has been shortened to bus in another application independently of its use with transit vehicles: a main connector in computer circuitry, originally an omnibus bar, became bus bar, and is now often just called a bus.
Ah, well, this magic bus. More to the point, this magic omnibus. Wherever it goes, it makes people think of busing (which I am careful not to spell bussing), be it in legislature, computers, books, or random bits of Latin such as mottos (Unus pro omnibus, omnes pro uno – Switzerland; Justitia omnibus – Washington DC; Omnia omnibus ubique – Harrods). It can thus be used for good or ill effect in dog Latin, such as this classic, meant to be understood in light of the English it sounds like:
Caesar adsum jam forte
Brutus et erat
Caesar sic in omnibus
Brutus sic in at
Sol sure don’t lucet on that omnibus (but Caesar did). Oh well, sick transit gloria…