disko

A disco is not a disko. This is the one thing to fix before anything else, because English speakers reach for the word and get it wrong. In Esperanto a discotheque is diskoteko and a nightclub in general is dancejo or noktoklubo. Disko never means the venue and never means the genre. It means a flat round thing, and its senses fan out from that: the shape itself, a gramophone record, the athlete's discus, a computer disk (malmola disko, lumdisko for a CD), and the cartilage between two vertebrae. All of them are circles.

The senses are worth separating. The primary reading in the dictionary is the geometric one, any flat circular object: la disko de la suno, the disc of the sun. The gramophone record is a specialisation of it, and in twentieth-century Esperanto texts it is the commonest sense by a distance, which is why the frequency list has this word where it does. Diskejo is a record shop, diskisto a DJ, surdiskigi to record onto a disc. In athletics you ĵeti la diskon, and the event is diskoĵetado.

No seam to find, and a good family to compare. Disk- is one root; there is no Esperanto prefix di- doing work here, and the -ko on the end is part of the root rather than an ending of any kind. Set it beside disketo, a floppy disk, which genuinely is disko plus the diminutive -et- and means a small one. That is the useful pair: one word where the pieces are real, one where they are not.