English is a tricky language. There are words that sound like one thing and mean another, loan words from other languages that can be hard to pronounce and grammar rules that can confuse. "Famous" and "infamous" are two words that can cause a lot of confusion and lead to problems in writing and talking. These two little letters added to famous mean a lot more than just “not famous.” Let’s clear up the confusion and make sure you’re using these words correctly and saying exactly what you mean.
"Famous" is a word that describes something or someone with a lot of influence and followers. Movie actors, singers, political leaders, monuments and cities can all be described as famous. The concept of fame and being famous, importantly, doesn’t have a value judgment attached to it.
A person can be famous for being a good and kind person, such as Keanu Reeves giving his salary for the Matrix sequels to the stunt and special effects crew. But you can also be famous for being really horrible, such as Jeffrey Dahmer achieving fame as a serial killer. They are both, however, famous. Being famous is less of an action, and more of a state of being.
The word "infamous", however, is more complicated than simply being famous or even famous for something bad. Unlike "famous," "infamous" has a connotation of being bad in reputation — shame and horror at whatever has happened is the name of the game.
"Infamy" is entirely negative and tends to refer to actions or people rather than a state of being. A prime example would be Pearl Harbor, which President Franklin Roosevelt referred to as “a day which will live in infamy.” FDR used the term as a way to allude to the massacre that happened on that day and describe it as an abomination.
If you look at the structure of the word, here the prefix “in-” means “having a negative or privative force.” Breaking down the word into its parts can help translate the meaning. Unlike "famous", "infamous" is specific rather than abstract, and overwhelmingly negative rather than positive; definitely not just “not famous.”