individuo

Three words compete for this space and they are not the same. Homo is a human being, a member of the species. Persono is a person, someone with a name and a face, and it is the everyday word: tri personoj atendis, three people were waiting. Individuo is the one-out-of-many word, and it is always implicitly measured against a group. It appears where the contrast matters: individual against society, one specimen against the population, one member against the committee.

Which is why it also carries the faint chill it has in English. Iu individuo staris ĉe la pordo sounds like a police report, not like a description of a friend, because calling a person an individuo deliberately declines to say anything else about them. Use persono for people you are being friendly about.

The etymology is worth keeping because it is still visible in Esperanto. Dividi is a live root on the site, and in- is the Latin negative that turns up in a dozen borrowed adjectives. Individuo is the undividable one. That is history rather than word building, though: you cannot make it from dividi inside Esperanto, and the derived forms you can make are individua (individual, as an adjective) and individueco (individuality).