Why does invisible mean not visible but infamous doesn't mean not famous

"Famous" used to mean "celebrated", or widely known for being good. "Infamous" is the opposite of that, so widely known for being bad. Due to linguistic drift, famous now just means that you've heard of them at all. Bonus: Have you heard that inflammable and flammable both mean "prone to burst into flame".

it comes from the latin root 'fama' which is less about just being known, but more particularly being known in \*good\* standing, or having a \*good\* reputation. So therefore the opposite of a good reputation, is a bad one. more confusingly, a while back infamous DID mean 'not well known' but that came from a different latin word, infamosus, which meant not well known in general. Middle English had infamis, which was closer to 'notorious' , and eventually these meanings sorta merged into our current 'infamous' moral of the story, the in-prefix is not before 'famous' necessarily, but before the latin 'fama'

Wait until you hear about flammable and inflammable

Because "infamis" is Latin for "bad guy," and "inflammare" is Latin for "to set on fire."

From Etymonline: > *Infamous* is from Medieval Latin *infamosus*, from *in-* "not, opposite of" + Latin *famosus* "celebrated". *Infamis* is from Latin *infamis* "of ill fame".

It kind of does mean not famous. Famous: known about by a lot of people (in a good way). Infamous: known about by a lot of people (but not in a good way). You are right in a sense that maybe it should just mean unknown but in this case the *in* is negating the *good* not the *known,* part of the meaning.

In Latin famosus meant "celebrated" and also "well-known". Because of these two somewhat different meanings, In the fifteenth century there were two words. There was "infamous" which mean "not well-known" and there was "infamis" which meant "well known for bad things". Those two almost identically pronounced words merged, leaving "infamous" meaning "well known for bad things" with "famous" meaning "well-known" but usually for good things.

In general, forming new words by adding affixes can be confusing/counterintuitive. This is because the logic applied can vary widely, and because affixes are often homophonous. Consider "consider" and "context" and "contraband" and "contort" and "connive" and "contour". They sound like they have the same root, but they don't. The outlier is "contraband" where the root affix is not "con," as in the other examples, but "contra," which is something different entirely. All this just to say—the best policy when questioning etymology is to look it up. :)

The prefix in- is better understood to be 'the opposite of' and not just 'not' The opposite of visible happens to simply be *not* visible. But the opposite of famous is to be widely hated, not to be unknown.

Don't rely on prefixes too much. Sometimes they are totally unrelated. Insane is the opposite of sane. Inexact is the opposite of exact. Indirect/direct, informal/formal. **But** inside isn't the opposite of side. It's the side that is within. Inflame isn't the opposite of flame; it's to *increase* a (metaphorical) flame. An insole isn't the opposite of your sole. It goes in your shoe, under the sole of your foot. There are just as many exceptions as there are words that conform to "in" being the opposite. --- I feel obliged to mention the famous Kenneth Williams quote; "Infamy, infamy, they've all got it in for me" https://www.youtube.com/watch?v=qZWTjQW49eg

See also: inflamable flammable

infamous does mean famous but not for good reasons

[Here](https://www.reddit.com/r/etymology/comments/6z33qp/why_is_it_called_infamous/) you go

Why does "beheaded" mean losing your head? Shouldn't the "be-" prefix mean gaining a head, as in bedecked or bejeweled? Shouldn't the word be "DEheaded"?