melankolio

Nothing in melankolio is built. The word looks as though it should come apart into pieces, and learners reach for a -ol- or an -oli- in the middle of it, but Esperanto has neither suffix. The root is the whole of melankoli-, taken in one lump from the international word, and the only ending on it is the plain -o.

The one genuine seam is the one nobody spots, and it is in Greek rather than in Esperanto: melas is black and kholē is bile. Ancient medicine held that four humours ran the body, and that too much of the black one made a person heavy and withdrawn. The theory is dead; the word survived it, and so did kolero (anger, from the same bile) in a language nobody expected to preserve Hippocrates.

It is not the ordinary word for sad. Malĝoja and malgaja are the plain, useful ones, and they describe a person with a reason. Melankolio is longer, slower and rather more literary: the settled, half-pleasant sadness with no particular cause that arrives with grey afternoons and old photographs. The adjective is melankolia and the adverb melankolie, both regular.