Ignatius wasn't the first one to use the word, but the oldest surviving writing using the word was from him, as far as I can tell. The Catholic Church was the only Church for the first 1000 years of Christianity. Then, in 1054 A.D., the Great Schism happened and the Orthodox splintered off. They retained Apostolic Succession, however, and therefore all seven Sacraments.
St. Ignatius of Antioch, the bishop of Antioch ordained and appointed by St. Peter, was captured by the Romans. While they were transporting him to be martyred for the faith, he wrote a letter to the Smyrnaeans around 107-110 A.D., referring to the "Catholic Church," not in such a manner as if he were coining the term, but in such a manner in which he fully expected the Smyrnaeans to understand what he was talking about.
It says in paragraph 8, "Where the bishop is present, there let the congregation gather, just as where Jesus Christ is, there is the Catholic Church."
See the entire letter here:
https://www.orderofstignatius.org/files/Letters/Ignatius_to_Smyrnaeans.pdf
The teachings of the Catholic Church contain the fullness of Divine Revelation, given by Christ to the Apostles, who gave it to their successors, the bishops, who did likewise now for about 2000 years.