Cattedrale vs. duomo
The Italian words cattedrale and duomo both translate to cathedral in English, but they have nuanced differences in usage and connotation.
Cattedrale
B1A cattedrale is the main church of a diocese, where a bishop is seated. It is a formal term used to denote an official ecclesiastical seat of authority.
La cattedrale di Santa Maria del Fiore si trova a Firenze.
(The Cathedral of Saint Mary of the Flower is located in Florence.)
La cattedrale è il centro della diocesi.
(The cathedral is the center of the diocese.)
Duomo
A2Duomo generally refers to a significant church that holds historical and cultural importance; it doesn't necessarily have to be the seat of a bishop. It often implies grandeur and prominence within the city, but may not always be used exclusively for diocesan cathedrals.
Il Duomo di Milano è uno dei simboli più famosi d'Italia.
(The Milan Cathedral is one of Italy's most famous landmarks.)
Torniamo al duomo per l'ultima messa del giorno.
(Let's return to the cathedral for the last Mass of the day.)
Ho sempre voluto visitare il Duomo di Siena, con la sua architettura gotica straordinaria.
(I have always wanted to visit the Siena Cathedral with its extraordinary Gothic architecture.)
Summary
While both cattedrale and duomo can mean cathedral, their usage differs. Cattedrale specifically refers to the principal church of a diocese, led by a bishop. In contrast, duomo often denotes a significant, grand church that holds substantial cultural or historical value within a city but does not necessarily serve as an episcopal see.