Anathema is a noun and in modern times it is used to mean a formal ban, curse or excommunication. It can also refer to someone or something extremely negative, disliked or damned. Curiously enough, the original Greek meaning for this word was 'something offered to the Gods'. So what happened?

Some quick definitions of the modern word from Merriam-Webster:

Definition of anathema
1 a :  one that is cursed by ecclesiastical authority
b :  someone or something intensely disliked or loathed —usually used as a predicate nominative
… this notion was anathema to most of his countrymen. — Stephen Jay Gould

2 a :  a ban or curse solemnly pronounced by ecclesiastical authority and accompanied by excommunication
b :  the denunciation of something as accursed
c :  a vigorous denunciation :  curse

Anathema derives from Ancient Greek: ἀνάθεμα, anáthema, meaning 'an offering' or 'anything dedicated', itself derived from the verb ἀνατίθημι, anatíthēmi, meaning 'to offer up'. That was its sole use.

Things changed when the Bible became involved. In the translation of the Jewish Bible known as the Septuagint the word is used to render the Hebrew word חרם (herem), and appears in verses such as Leviticus 27:28 to refer to things that are offered to God and so banned for common (non-religious) use. The Hebrew word was also used for what was devoted, by virtue of a simple vow, not to the Lord, but to the priest. In postexilic Judaism, the meaning of the word changed to an expression of God's displeasure with all persons, Jew or pagan, who do not subordinate their personal conduct and tendencies to the discipline of the theocracy, and must be purged from the community—thus making anathema an instrument of synagogal discipline.

The noun occurs in the Greek New Testament six times. Its meaning in the New Testament is disfavor of God, a meaning that, according to Vine's Complete Expository Dictionary of Old Testament and New Testament Word, in Acts 23:14 to the sentence of disfavor, and in the other instances to the object of God's disfavor.

Since the time of the apostles, the term 'anathema' has come to mean a form of extreme religious sanction, known as excommunication. The earliest recorded instance of the form is in the Council of Elvira (c. 306), and thereafter it became the common method of cutting off heretics. When the authority of Rome was split in the Great Schism between Eastern and Western churches in 1054, an anathema was issued by Rome against the Eastern Patriarch who then issued another one against the cardinal who delivered it.