papo

The ladder, from the bottom. A pastro is a priest, the one who takes the service in a parish. An episkopo is a bishop, who has charge of many parishes. A papo is the pope, the bishop of Rome, and there is one at a time. Esperanto keeps the three words as distinct roots, as English does, and none of them is built from the others. Kardinalo, abato and monaĥo fill in the rest of the structure; pastro is by far the commonest of the set in ordinary text.

Register. Papo is an encyclopedic word rather than a devotional one. It is what an Esperanto newspaper, an atlas or a history book calls the office, and it carries no reverence of its own - you can write la papo mortis as flatly as la reĝo mortis. Capitalisation follows the usual rule: lowercase for the common noun, a capital when it stands in for a name, la Papo. The adjective is papa (papal) and the office is papado or papeco.

The near-pair you must not fall into. Papo is not paĉjo. Paĉjo is dad, built inside Esperanto from patro plus the affectionate -ĉj-, and it belongs at a kitchen table. Papo belongs in Rome. Two letters and a hat separate them, and the irony is that they were once the same idea: Greek pappas was itself a nursery word for father, the noise a small child makes. Latin promoted it to a title, Esperanto borrowed the title, and then built its own nursery word from scratch. Watch papero as well - paper, one syllable longer, and a common slip in dictation.