In Newtonian mechanics, the space of states is called "phase space" for reasons that are pretty mysterious.
A mystery that hadn't occurred to me before, probably because the German word "Zustandsraum" means literally "state space," so no mystery there. Stefan and I were guessing Gibbs, who introduced the word, might have generalized the terminology from the harmonic oscillator where the location in phase space does indeed tell you the phase of the oscillation. (You find a nice applet depicting the phase-space diagram of the damped and undamped oscillator here).
In any case, this caused me to ponder what other words with funny origin physicists like to use. (Both funny ha-ha, and funny peculiar.) Why, for example, is the recombination in the early universe called recombination if there was no prior combination? Not that I was the first to ask that question. Sean offered the explanation that the word is borrowed from nuclear physics. But then why don't nuclear physicists call the fragmentation refragmentation?
There are more interesting nomenclatures though than presence or absence of prefixes.
A particularly well known oddity is the name "quarks" introduced by Gell-Mann, who couldn't decide how to spell the sound ducks make:
In 1963, when I assigned the name "quark" to the fundamental constituents of the nucleon, I had the sound first, without the spelling, which could have been "kwork". Then, in one of my occasional perusals of Finnegans Wake, by James Joyce, I came across the word "quark" in the phrase "Three quarks for Muster Mark". Since "quark" (meaning, for one thing, the cry of the gull) was clearly intended to rhyme with "Mark", as well as "bark" and other such words, I had to find an excuse to pronounce it as "kwork".
~M. Gell-Mann, The Quark and the Jaguar, via Wikipedia
Had Gell-Mann read a German dictionary instead of Joyce, he'd have noticed "Quark" is the German word for a milk product (often mistakenly translated as "cottage cheese" which is something entirely different). Besides this, "Quark" is a frequently used colloquial expression for nonsense.
But at least we know how that word came along. A mystery remained to me why the English adaption of the German word "Eigenvektor" came out to be "eigenvector." The German word "eigen" simply means "innate," and could easily have been translated.
A better example fo imaginative nomenclature is the Psi-particle (now known as J/Psi) whose cloud-chamber pictures frequently have the shape of a Psi (see picture above).
Then there is the "Penguin diagram", which owes its name to a lost bet and some illegal substances, and the "tadpole diagram" which once run risk of turning into a "spermion." Probably a good thing the tadpoles kept their name - just imagine what issues the anti-abortionists would have had with spermion cancellation.
In General Relativity, we have the conjecture of "cosmic censorship" to prevent us from seeing "naked singularities," and "wormholes" are already a classic. Cosmologists have further blessed us with MACHOs and WIMPs, acronyms for MAssive Compact Halo Object and Weakly Interacting Massive Particles respectively. Loop Quantum Gravity features a LOST theorem, after the last names of its authors. The large gap between the energy scale of currently known physics and the scale where grand unification is thought to occur is also known as "desert." We have a seesaw mechanism, play with Mexican hat potentials, have ghosts and talk about stop particles. There's a swiss cheese universe and neutron stars have pasta-antipasta layers with a spaghetti-phase. The most stupid nomenclature I so far have come up with is a "pullover". Yes, I know, not terribly original, but then I didn't expect a Nobelprize for it ;-)
Did I miss something? Leave it in the comments!