prepozicio

A metalanguage word, and one of the small set that lets you talk about Esperanto in Esperanto: substantivo, adjektivo, verbo, adverbo, prepozicio, konjunkcio. They all arrived from the Latin grammatical tradition intact, which is why an Esperanto grammar reads as if you already know the vocabulary.

Why prepositions are the easy part here and the hard part elsewhere. The design rule is that each Esperanto preposition has exactly one meaning and keeps it. En is in, sur is on, kun is with, per is by means of, pri is about, and none of them drifts into idiom the way English on does between on Tuesday, on fire and on purpose. That single decision removes most of what makes prepositions the last thing a learner of French or German gets right. The full set is laid out in Esperanto prepositions.

And then the awkward corners. Je is the deliberate escape hatch, the preposition with no meaning of its own, kept precisely so the fixed-meaning rule does not have to be bent; po distributes a quantity; da measures; and the accusative -n turns en la domo into en la domon and changes position into direction. Those are the ones worth a second pass: the tricky prepositions.

The third piece is which preposition a given verb wants after it, which is a property of the verb rather than of the preposition. That is verb government, and it is where a learner who has understood every preposition individually can still write atendi por and be wrong.