I was thinking about the words ‘factoid’ (a statement based on assumption) and ‘fact’. Are these words unrelated or is -oid a bound morpheme in this case? If it is a morpheme, what exactly does -oid mean and what is its origin? I wonder if words like ‘humanoid’ and ‘cannabinoid’ are related.
Factoid is rare word in that it’s a relatively popular recent coinage, but unlike most slang, can be traced to a single, possibly uncontested point of origin:
The earliest record of factoid comes in 1973, in Marilyn, a book that was a combination of photographs of Marilyn Monroe and biographical text provided by [Norman] Mailer. Shortly after using the word Mailer helpfully added an explanation: “…that is, 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.”
Prescriptivism isn’t going to serve us well here – I’m not going to say that the definition you’ve provided is wrong, but it is not the definition used by the word’s originator. When Mailer chose the -oid suffix, he did so in accordance with his definition of the word.
Trying to explain Mailer’s thinking, Merriam-Webster suggests,
[factoid] hails from a long line of words created through adding the suffix -oid, which comes from the ancient Greek eidos, meaning “appearance” or “form."
A key point, which this article hints at, but does not state, is that -oid words often describe a thing which resembles, but is not actually some other thing. This is not always the case. Cannabinoids are present in cannabis; the deltoid muscle really is (roughly speaking) a triangle; amoeboid and amoeba are used interchangeably. But consider that an asteroid is like a star, but is not one; an android is an imitation man; something that is humanoid is similar in form to a human. Likewise, a factoid resembles a fact, in that it’s an idea that people think is true, but it is not. Or at least, that’s what Mailer was probably thinking when he made up the word.