Some Catholics bridle at the modifier “Roman,” noting that it has derogatory origins, but I think that there’s much to be said for what then-Fr. Joseph Ratzinger had to say about the label fifty years ago:
In that it says “Catholic” it is distinguished from a Christianity based on scripture alone, instead acknowledging faith in the authority of the living word, i.e. in the office of the apostolic succession. In that it says “Roman” it firmly refers this office to its center, the office of the keys vested in the successor of St. Peter in the city consecrated by the blood of two apostles. By uniting the two to say “Roman Catholic” it expresses the pregnant dialectic between primacy and episcopate, neither of which exists without the other. A church which wished to be only Catholic, having no part with Rome, would thereby lose its Catholicity. A church which, per impossibile, wished to be only Roman without being Catholic would similarly deny herself and degenerate into a sect, ‘Roman’ guarantees true Catholicity; actual Catholicity attets Rome’s right.
Joseph Ratzinger, Primacy, Episcopate, and Apostolic Succession in Rahner & Ratzinger, The Episcopate and the Primacy 62 (Barker et al. trns. 1962).