Bona fides looks like a plural word in English, but in Latin it is a singular noun that literally means "good faith." When bona fides entered English, it at first stayed very close to its Latin use, and it also kept its singular form—for example, "a claimant whose bona fides is unquestionable." But in the 20th century, use of bona fides began to widen, and it began to appear with a plural verb in certain contexts, such as "the informant's bona fides were ascertained."