To make a solemn oath. Traditionally a solemn declaration or affirmation was pronounced as being by some sacred being or object. This practice is perpetuated in modern courtrooms by swearing in witnesses, a procedure that involves laying their hands on a Bible and pronouncing “Do you swear to tell the truth, the whole truth, and nothing but the truth?” Swearing on an entire stack of Bibles thus is construed as carrying considerably more weight than swearing on just one book. An American colloquialism from the mid-nineteenth century, it was used by Billie Holiday in her 1956 memoir, Lady Sings the Blues: “Mom . . . swore on a stack of Bibles I was eighteen.”