1,024. Whom a Kohein May Not Marry
145:11 One may not remain with his wife even for an hour without a kesubah (marriage contract). If she loses her kesubah, he must go immediately to the beis din to have another written for her.
145:12 A kohein is not permitted to marry a divorcee, a "zonah*," a "chalalah," or a woman who has had chalitzah performed.** A zonah includes even one who was intimate with a forbidden relationship against her will; nevertheless, she is halachically considered a zonah and it is forbidden for a kohein to marry her. A chalalah is the daughter of a kohein with a woman who is prohibited to him.
*Colloquially, people use the word "zonah" to mean a prostitute. Halachically, the word means a woman who has had sexual relations with a man whom she would be forbidden to marry. Premarital sex with someone she could marry does not render a woman a zonah.
**Chalitzah is the ceremony that separates a widow from her deceased husband's brother. A woman who has undergone this ceremony, called a "chalutzah," is the functional equivalent of a divorcee.