konkreta

A false seam, and a good one. Konkreta looks like it is built from kon- and kreto, and a learner who has just met the affix system will try to cut it there. It is not. Concrete is not with-chalk. The word arrived whole from Latin concretus, and kreto (chalk) is a separate Latin word, creta, that has nothing to do with it. Cut this one at the seam and you get nonsense.

And its twin does the same trick. Diskreta at rank 2,708 in this same chapter is the identical trap: not dis- plus chalk either, but Latin discretus from discernere, to separate out. Two words, ten ranks apart, both ending in what looks like the same root, and the sources are three different Latin words: crescere to grow, cernere to sift, and plain creta for chalk, whose own origin is disputed and may or may not lead back to cernere as well. This is exactly why the rule is that you decompose an Esperanto word only when the meaning comes out right. Kon- is not even an Esperanto prefix.

It never means the building material. English overloads concrete with the grey stuff that sets in a mould; Esperanto does not. That is betono, a separate root, and calling a pavement konkreta will get you a puzzled look. Konkreta is only ever the opposite of abstract: a konkreta ekzemplo, a konkreta propono, a konkreta rezulto. The noun is konkretaĵo, a concrete thing, and konkretigi is to make something concrete, which is the verb every committee needs and few use.