Comment Re: You keep using that word. I don't think it mea (Score 2) 45
"Penultimate" isn't a synonym for "ultimate"—it means the thing before the ultimate. Likewise we have penumbra for the blurry edge of a shadow (umbra). This results in some truly special words like "antepenult," meaning "the thing before the thing before the final thing," commonly used when discussing where the stress/accent falls in a Greek or Latin word.
"Invaluable" does indeed mean "not able to be valued" when analyzed morphologically, but the standard usage of it is indicating something is beyond value, i.e. infinitely or inestimably valuable. A value of zero is still a value, after all.
"Inflammable" however actually means "able to be inflamed," as in "put in flame" or "set on fire." The confusion comes from assimilation of the Latin preposition "in" (which we have as "in" or "on") instead of the more typical prefix "in-" (which demarcates negation.) You don't have to look very far for other words where "in" doesn't mean "not": indicate, inherit, imply, investigate, indict, involve...