Anathema, adj and n. Consecrated and holy. The term originally denoted
a special offering hanging in a temple, and has come to mean a degree
of holiness which borders on superlative.

The Supreme Being is the most holy; the angels in his presence shield
their faces so that they will not see him and be destroyed. Secondary
to this is a degree of holiness such that anything which touches it
must be destroyed. The Ark of the Covenant was holy; it was to be
carried only with poles, and when Uzzah touched it in order to steady
it, he was destroyed. The book of Joshua records an entire city of
such sanctity that it was anathema; Achan stole goods from it, and
fierce anger burned against the whole nation of Israel until he was
destroyed.

It is possible for this sanctity to be conferred by benediction; one
form used contains the words, "Let him be anathema..." That is to say,
a person as well as an object can be so sacred and holy as to be
anathema.

Commonly, this benediction is bestowed upon other believers. The
present unity of the church is so complete that it is frequently
bestowed upon other Christians whose beliefs legitimately differ
slightly, and almost never bestowed on heretics.

-- Hayward's Unabridged Dictionary