kuriero

A false seam with a true story behind it. Kuriero looks like kuri, to run, plus -er-, the suffix for a single small particle of something (sablero a grain of sand, monero a coin). A runner-particle is nonsense, and that is the giveaway: -er- makes tiny pieces, not people. The suffix for a person is -ist- or -ul-, so a made-up Esperanto word for a runner would be kuranto or kuristo, never kuriero.

But the resemblance is not pure coincidence, and this is what makes the word worth a paragraph. Kuri came into Esperanto from Latin currere, to run. Kuriero came in from French courrier, which also came from currere. They are cousins who arrived in the language separately, two centuries and one border apart, and the family likeness survived the journey. The seam is false as Esperanto morphology and genuine as Latin history - exactly the situation salato is in a few ranks further down this same band.

Usage. Kuriero is the person or the service; kurierservo is a courier firm. The historical sense - a rider carrying despatches - and the modern one - the person at the door with a parcel - are the same word, which is why the third example above still reads naturally.