plenluno

Two words you have had since the first hundred.Plena at 223 is full, luno at 897 is the moon, and plenluno is what happens when you push them together. Notice what the compound does that the loose phrase does not: plena luno is a description, a moon that happens to be full, while plenluno is the NAME OF A PHASE, a fixed point in a calendar. Both are correct Esperanto and they are not interchangeable in a sentence about dates. The rest of the set builds itself: novluno is the new moon, duonluno the half moon, lunlumo moonlight, and luna is the adjective for anything to do with it.

The word drags a whole folklore behind it. Every European language attaches the same superstitions to this phase - madness (English has lunatic from the same Latin luna), sleeplessness, hair that grows faster, and the night when things that are usually people are not. Esperanto handles all of it by compounding on the spot from roots you already own: a lupo at 1,066 crossing a field, a vesperto at 2,684 cutting across the disc, a churchyard full of ombroj. You do not need a special vocabulary to write a ghost story in this language. You need about nine nouns and the nerve.

And it is the word this chapter's story is named after.La plenluno is the milestone reader for chapter 30, and it uses the moon for exactly what the moon is for in fiction: enough light to see something by, and not enough to be sure what you saw.