nomumi

Decode it: nom- plus -um- plus -i. Nomo is a name. -Um- is the suffix with no fixed meaning, the one that says only "some relation to the root, and you will have to be told which". Put them together and you get nomumi, which is not to name a thing but to appoint a person: to put somebody's name against a post.

Why -um- is here at all, and why that is the point. Esperanto could not use plain nomi for this, because nomi already means to call something by a name (ili nomis la infanon Petro). The language needed a second, narrower verb, and there was no honest affix for the job: appointing is not making-something (-ig-), not becoming (-iĝ-), not a container, not a place. -Um- is precisely the escape hatch for that situation. The -um article makes the general case: -um- guarantees nothing, so every -um- word has to be learned as a word. This is one of the ones worth learning.

The company it keeps. Kolumo is a collar from kolo a neck. Butonumi is to do up buttons. Kalkanumo is the heel of a shoe from kalkano the heel of a foot. Amindumi is to court somebody. Plenumi is to fulfil. Akvumi is to water the garden. Notice how little the set has in common: that is the suffix working exactly as designed, and nomumi sits comfortably inside it.

In use. Transitive, and the post goes either as a bare predicate (nomumi ŝin direktoro) or with al and the office (nomumi lin al la posteno). Nomumo is the appointment itself, and eksnomumi is not a word: to remove somebody you eksigi them. The neighbouring verb is elekti, to elect or choose, and the difference is real - a committee elektas its own chair and nomumas somebody else's officer.