bleki

Bleki is the general one. It is the noise an animal makes, whichever animal it is, and English has no single word for that at all: we have to pick bleat or bray or low or neigh before we can open our mouths. Esperanto lets you say the category and stop.

That generality is what makes it useful when you do not know the specific verb, which is most of the time. And when you do want to be specific, the language builds rather than borrows: ŝafbleki is what a sheep does, ĉevalbleki what a horse does, ranbleki what a frog does. Root plus bleki, and you are done.

Two siblings on this course are specific verbs in their own right rather than compounds. Boji, rank 1852, is a dog barking. Muĝi, rank 2257, is the deep one: cattle lowing, and by extension the wind and the sea. Everything else you can reach with bleki and a compound.

The wider system is worth reading whole once, because Esperanto turns noises into verbs on sight: see Ho, Nu, Ve: the little words that carry the feeling, which sets bleki alongside boj, miaŭ, bum and the rest, and shows the rule that makes them all work.