der Christ
Christian
A person who belongs to the Christian religion and believes in Jesus Christ.
Er ist ein gläubiger Christ und geht jeden Sonntag in die Kirche.
He is a devout Christian and goes to church every Sunday.

Christian
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Christian
A person who belongs to the Christian religion and believes in Jesus Christ.
Er ist ein gläubiger Christ und geht jeden Sonntag in die Kirche.
He is a devout Christian and goes to church every Sunday.

Important related words are derived from 'Christ' (Christian): the adjective 'christlich' (Christian, e.g. Christian values) and the noun 'das Christentum' (Christianity) for the religion itself.
Das Christentum ist eine der großen Weltreligionen.
Christianity is one of the major world religions.
To express the degree of religiosity, 'Christ' (Christian) is often combined with adjectives such as 'gläubig' (devout), 'praktizierend' (practicing), or 'überzeugt' (convinced).
Sie ist eine praktizierende Christin und engagiert sich in ihrer Gemeinde.
She is a practicing Christian and is active in her parish.
The expressions 'vor Christus' (before Christ/BC) and 'nach Christus' (after Christ/AD) are fixed terms in historiography. In texts, they are often abbreviated as 'v. Chr.' and 'n. Chr.'.
Die Pyramiden von Gizeh wurden lange vor Christus erbaut.
The Pyramids of Giza were built long before Christ.
Catholic
'Christ' (Christian) and 'Katholik' (Catholic) both refer to religion, but they are not the same. A Christ belongs to the Christian religion. A Katholik is a Christian who belongs to the Roman Catholic Church. So 'Christ' is the broader term, while 'Katholik' is more specific. Learners may confuse the words because Catholics are also Christians. But not every Christian is a Catholic; for example, there are also Protestants. If only the religion in general matters, 'Christ' is the right word. If the specific church matters, use 'Katholik'.

Tom ist Christ und geht an Weihnachten mit seiner Familie in die Kirche.
Tom is a Christian and goes to church with his family on Christmas.
Im Gespräch erzählt Herr Schneider, dass er Katholik ist und zur katholischen Gemeinde gehört.
In the conversation, Mr. Schneider says that he is Catholic and belongs to the Catholic parish.