traktato

A fused word, not a built one. Traktato looks like trakti at rank 1,051 plus the passive participle -at- plus -o: the thing being dealt with. That reading is close enough to the truth to be useful and it is not how the word got here. Traktato came into Esperanto whole from Latin tractatus, where the -at- was already a Latin participle suffix that had hardened into part of the noun centuries before Esperanto existed. The seam is real history and dead grammar: you can see it, you cannot cut on it.

The -ato fossils, as a class. This is a recurring shape in the borrowed layer and it pays to recognise it rather than to be caught by it each time. Rezulto at 1,030 hides a Latin participle the same way; so do kandidato, advokato, delegato, mandato and soldato. In every case a Latin -at- has fused, and in every case Esperanto's own live -at- is a different thing that happens to be spelled alike. The scientific Esperanto article makes the general rule: international roots arrive whole and do not obey the cutting rules that native compounds do. Compare traktita, "dealt with", which is the live participle actually built from trakti, and which means something quite different from traktato.

Against kontrakto. Kontrakto at 1,349 is a contract - any binding agreement, between people, firms or states. A traktato is specifically between states, and it is the word in la Traktato de Versajlo, la packontrakto argument, and every history lesson about the twentieth century. A landlord and a tenant sign a kontrakto; France and Germany sign a traktato. Trakti itself, usefully, also means to negotiate, so trakti pri traktato is a real and non-circular sentence.