scenaro

This one is a genuine seam, and it is the rarer case. Most of the words in this band look assembled and are not. Scenaro is the opposite: it looks borrowed, and it also parses.

scen + ar + o

Sceno is a scene, at rank 1,505. -Ar- is the collective suffix, the one that turns arbo into arbaro, a forest, and homo into homaro, humanity. So a scenaro is the set of scenes - which is exactly what a screenplay is. The word means what its parts say it means.

And the international word agrees. Italian scenario came from Latin scaenarium by an entirely separate route, arrived in French and English as scenario, and lands letter for letter on what Esperanto would have built anyway. Two roads, one destination. That does happen - -ismo words behave similarly - and when it does, nobody has to choose: the borrowing and the build reinforce each other and the word is unusually easy to remember. Note that this is luck rather than design. Arkitekto, six ranks earlier in this same chapter, is what happens when the luck runs out.

Two senses, both current.

• The document. A screenplay or a script: filmscenaro, verki scenaron, la scenaro de la teatraĵo. The writer is a scenaristo.
• The hypothetical. The way events might unfold, exactly as English uses scenario in a report or a meeting: la plej malbona scenaro, the worst case; du eblaj scenaroj, two possible scenarios.

The second sense is the newer one in every language that has it, and it is the one you are most likely to write. The collective parse still works for it, if you squint - a scenario is a sequence of scenes that have not happened yet.

Do not confuse it with sceno. A sceno is one scene: one continuous stretch of a play or a film, or the visible situation in front of you. The scenaro is the whole set of them, on paper. Scenejo, with the place suffix, is the stage itself.