(rare) Whom is.

As the object of a verb. / As the object of a preposition. / (relative) Used to refer to a previously mentioned person or people.

(politics) Who will defeat or dominate whom? A Bolshevist principle or slogan, urging action against the capitalists.

Used as a formal salutation in a letter when the writer does not know who will read the letter.

Synonym of to whom it may concern