>but what of words used once, are oncewords words if they had meaning, as these did, for just one other person?

I'm not sure how serious your question is, but you have pretty much defined a nonce word, which is a word invented for (and expected to be used only for) a special occasion; i.e., for the nonce. some nonce words surprise the inventor, catching on and thereby disqualifying themselves from the description.

then there is the phrase hapax legomenon [Gk, something said only once], a word evidenced by a single citation.

(thus there is a distinction: a nonce word is identified by intent; a hapax is distinguished by evidence -- or lack thereof. :)