gejo

Gejo is a gay man, and by extension a gay person. The adjective is geja: geja paro, a gay couple; geja flago, a rainbow flag; gejaj rajtoj, gay rights. A gay woman is more usually lesbo or lesbanino.

The word is a straightforward borrowing from English, and it arrived late. Esperanto's own home-grown term is samseksemulo - sama same, sekso sex, -em- inclined to, -ul- person - which is precise, transparent and slightly clinical, rather like "homosexual" in English. Both are in use and neither is rude; gejo is the everyday one, samseksemulo the formal or careful one. Malgeja, straight, is built the way you would expect, though most speakers say heteroseksema or simply rephrase.

A false seam worth naming. Ge- is a real Esperanto prefix meaning "of both sexes together": gepatroj parents, gefratoj siblings, gesinjoroj ladies and gentlemen. Gejo has nothing to do with it. There is no root -jo, and the ge at the front is just the first two letters of an English word. As with benzino, the affix only counts when the remainder is a root you could meet alone.

That accident is a useful way into a bigger question: Esperanto's default assumption that a person-root is male until you add -in- is the language's most argued-over feature, and there are live proposals to fix it. The gender in Esperanto article lays out the system, the criticisms and the reforms, and this word sits in the middle of that conversation.