mojosa

Cool, as in good. Not cold. Esperanto had malvarma for the temperature and nothing at all for the other sense, which is the gap mojosa was built to fill.

We know exactly where it came from, which is almost unheard of. It was made in November 2003, at a youth seminar in Söjtör, Hungary, by Gregor Hinker, Felix Zesch, Carl Mäsak and the rest of the room. The construction is an acronym padded into pronounceability: Modern, Jun, Stil - the initials of modern-, jun- and stil- - vowels between them, -a on the end, M-o-J-o-S-a.

It took. It inflects like any other adjective (mojosa, mojosan, mojosaj, mojosajn), and it has grown a family: malmojosa for uncool, mojose for the adverb, mojoseco for coolness, mojosulo for the person who has it. That is the acid test for a coinage - not whether people say it, but whether the language's machinery starts running on it.

And the honest caveat. It is not in PIV, and a speaker in their seventies may genuinely not recognise it. Both of those are true at once and neither is a scandal; it is simply what a living colloquial layer looks like from inside. Our advice, and it is the same advice the spoken Esperanto article gives: use it with speakers under about fifty, expect blank looks above that, and above all recognise it and enjoy it when it turns up.

Why a learner should care about a slang word at all. Not for mojosa itself. For what it proves: the word-formation system is not a museum exhibit. Somebody used it on a Tuesday night in 2003 and the language absorbed the result.