The word anathema (Strong's Concordance #G331) is used six times in the original language of the New Testament. It is recorded in Acts 23:14, 1Corinthians 12:3, 16:22, Romans 9:3 and Galatians 1:8 - 9. Anathema, which means cursed or accursed, is utilized in the Apostle Paul's double condemnation of anyone, be they angel or human, who dares promote a false gospel.
For I could wish that myself were accursed (anathema) from Christ for my brethren, my kinsmen according to the flesh: (Romans 9:3, KJV).
But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed (anathema). As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed (anathema, Galatians 1:8 - 9, KJV).
The most well known use of the literal word is in the King James Bible book of 1Corinthians.
If any man love not the Lord Jesus Christ, let him be Anathema Maranatha (1Corinthians 16:22, KJV).
Other Bible translations such as the Douay-Rheims, Young's Literal Translation and the American Standard Version also use the literal word within their text.
Apostle Paul's Usage
Paul used anathema as part of a test of truth to determine whether someone is inspired by God's spirit or not.
Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed (anathema): and that no man can say that Jesus is the Lord, but by the Holy Ghost (Spirit) (1Corinthians 12:3, KJV).
Apostle Paul knew from personal experience the seriousness of defaming the only name given through which a person can be saved (Acts 4:10 - 12). Before his conversion, when he was persecuting the true church, he forced believers to blaspheme or curse Christ in order to save themselves (Acts 26:11).
Heretics and Heresy
One of the earliest religious uses of this word outside the New Testament took place in 431 A.D. It was in this year that Cyril of Alexandria proclaimed 12 anathemas or curses against a heretic named Nestorius. By the 6th century A.D., the Catholic Church was using the word to designate a formal ecclesiastical curse against certain teachings or those it thought were heretics (Encyclopedia Britannica). Those who were declared anathema were excommunicated from (thrown out of) the church.
Pushback
The Roman Catholic Council of Trent, held in three parts from 1545 to 1563 A.D., was assembled to bolster the church's response to the growing Protestant Reformation.
The council's dogmatic definitions of doctrines clarified the majority of its beliefs that were contested by the Protestants. Their vigorous defense of the church's teachings resulted in delineating almost 150 beliefs and practices as being anathema.
The Council of Trent defined what it considered heresy (anathema) in areas such as justification before God, the Catholic Mass, and the church's seven sacraments (baptism, confirmation, the Eucharist, penance, anointing of the sick, holy orders and matrimony). Those who took part in the council were obliged to sign all the decrees that were officially adopted. Those who refused to sign were themselves under a threat of being excommunicated!