When Norman Mailer used factoid in his 1973 biography of Marilyn Monroe—the first known written instance of the word—he conveniently included its definition, too. Factoids, he explained, were “facts which have no existence before appearing in a magazine or newspaper, creations which are not so much lies as a product to manipulate emotion in the Silent Majority.”
In other words, factoids were an early version of fake news: erroneous tidbits that people believed because they seemed like they could be facts. This interpretation of the term, which Mailer may have coined himself, matches the meaning of the suffix -oid. As explained in the Oxford English Dictionary, -oid is usually used in science to denote “something having the form or appearance of, something related or allied in structure, but not identical” to its root word. You might use the word humanoid, for example, to describe Bigfoot or Star Wars’s C-3PO; both resemble humans, but they’re not actually humans.
Over time, as society developed an insatiable appetite for fun facts in every form—fact-a-day calendars, trivia nights, Jeopardy!, etc.—people started co-opting the word factoid to mean “a brief or trivial piece of information.” According to Merriam-Webster, a possible reason for this shift might be that we simply don’t have a good term for trivial fact. Some have floated factlet as an option, since the suffix -let essentially means little, but neither Merriam-Webster nor the Oxford English Dictionary has given it an official entry (perhaps because few people actually use the word).
At this point, the definition of the word factoid is an ongoing debate between linguistic prescriptivists and descriptivists. The former believe only Mailer’s original definition is correct, while the latter think the definition should reflect how people currently use the word. For the record, Merriam-Webster and the Oxford English Dictionary list both definitions.
But if someone tells you a factoid, you might want to ask how they personally define the term before you accept their factoid as fact.
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