peniso

Peniso is the anatomical word and it sits in exactly the register of mamo and stomako: a doctor's term, neutral, printable, usable in front of anyone. Esperanto has no Latin-versus-Anglo-Saxon split the way English does, so there is no polite alternative to reach for and none is needed. It is the word a textbook uses and the word a clinic uses. The body vocabulary the course teaches is collected in La korpo, along with the rule that catches English speakers out: Esperanto puts la where English puts a possessive, so li lavis la manojn is he washed his hands.

The related terms are built the way everything else is. Sekso is sex in both the biological and the grammatical sense, seksa the adjective, and seksorgano the general term for a sex organ. Urino names what passes through, and the word for the tube that carries it is uretro. Vira is the adjective for male and ina for female, so a vira seksorgano needs no further explanation.

The etymology is worth a line because it is not obscene at all. Latin penis meant a tail long before it meant anything else, and the tail sense is where the diminutive peniculus, a little brush or a painter's tuft, comes from. That gives penicillus, and from penicillus English gets both pencil and, by way of the brush-shaped spore clusters Alexander Fleming's mould grows in, penicillin. Three English words from one Latin tail.