In his lengthily-titled 2004 book, The Right Word in the Right Place at the Right Time: Wit and Wisdom from the Popular "On Language" Column in The New York Times Magazine (whew!), the late pundit William Safire considers the difference between the words celibate and chaste. He admits to having once erred in a comparison of those words when he said (correctly) said that celibate means “unmarried,” but defined chaste (wrongly) as “refraining from all sexual intercourse.”
Chaste (from the Latin castus, meaning “pure”) actually means abstention from unlawful sexual activity. It is most commonly thought of as meaning no sex except between married partners. But—like what the meaning of is is—the definition of unlawful has many interpretations.
In civil law, illicit sexual activity may be variously defined in different jurisdictions. Adultery, for example, is perfectly legal in most European countries, but it is severely punished, with penalties including death, in some Middle Eastern lands. Adultery is illegal (though rarely prosecuted) in most U. S. states, but the offense is defined differently in North Carolina than it is in New York.
Doctrines of certain religious groups permit practices (polygamy, say) that others regard as unlawful. Some religions permit same-sex marriages, while others require celibacy of their clergy. So before you can try to be chaste, you have to know whose laws you’re living under.
The cultural historian Jacques Barzun (who, incidentally, celebrates his 103rd birthday tomorrow at his home in San Antonio) goes a step further in defining chaste. He is quoted by Safire as saying: “It is quite possible to be unchaste in marriage—by excessive sexual indulgence, perpetual search for means to heighten pleasure, and anything like animal violence that disregards the partner…”
Celibate, from the Latin word for “unmarried”—caelibatus—is also loosely used sometimes, especially when applied to a religious vow, to mean abstaining from all sexual intercourse.
The Bard of Buffalo Bayou recalls the young Catholic priest who, after taking his final vows, complained: “Now you tell me! I thought that word was celebrate.” The Bard can usually tell one word from another, as you may judge from the following scurrilous screed:
A young lady of questionable taste
Said “yes” with unseemly haste
When invited to bed,
Because, as she said,
She’d rather be chased than chaste.