The phrase bona fide comes directly from the Latin bona fides, which means, roughly, good faith. In modern English, bona fide (without the s) is usually an adjective meaning (1) made or carried out in good faith or (2) real or genuine. Bona fides, with the s at the end, is a noun meaning (1) good faith, (2) credentials, or (3) information that establishes a person’s reputation or credentials.
The Latin bona fides is singular, yet writers in English almost always treat it as plural. Bona fide, meanwhile, was originally a legal term meaning without fraud, and it was an adverb. It developed its modern meaning through centuries of what was once seen as misuse.
If you do use either of these terms, don’t forget to make it two words (and bonified is not a word recognized by dictionaries). There’s no need to italicize these long-established loanwords in normal use.
Here are a few examples showing how the terms are conventionally used in this century:
While Kim is a bona fide mogul worth a reported $35 million, her fiancé isn’t bad off either. [Los Angeles Times]
The Liberal party must earn its modern economic bona fides and not rest on past laurels. [National Post]
By now, they are bona fide celebrities, with their own branded trainers, energy drinks and bobble-head dolls. [Guardian]
It’s a sign of the times that the more conservative Romney 2.0 is having to defend his ideological bona fides. [New Republic]
The German board game has become a bona fide social phenomenon. [Globe and Mail]
Those back-slapping bona fides are helpful now that the feds are weighing a host of new rules that has bankers itchy. [Wall Street Journal]