The Truth About Cats and Dogs

Why do you suppose Felix is such a stereotypically cat name and Fido likewise for dogs?

Fido's the easy one to answer: it's from the Latin "fides", meaning "faith". What's more faithful than a dog? "Fides" has plenty of offshoots in English. Direct from Latin we have "bona fide", "in good faith", and by extension "genuine". (If I never see "bonified" again it won't be too soon.) We have "fidelity", meaning "faithfulness" in several senses such as the sexual fidelity of monogamy and the accuracy of high-fidelity stereo sound. There's "fiduciary", "holding in trust" in a financial sense, and "confide", to trust with a secret. We have "infidel", someone who isn't of the speaker's chosen faith, and "perfidious", "treacherous", literally "destructive of faith".

Felix is trickier, and my best guess is that it's a sort of joke based on the Latin word for cat, "felinus". They must be related--they start with the same four letters! They aren't, though. "Felix" is the Latin word for "happy", and this is the sense it which in appears in English--once again, though, sometimes modified through analogy (as in "a felicitous coincidence"). Perhaps "felix" didn't get nearly as many words into English as "fides" did because we absorbed a huge number of happy-words from other languages: joyful (from French), lusty (from German), thrilling (spontaneously generated within Old English), and on and on.

Not that cats aren't happy creatures generally, mind you. But if I were picking a descriptive name for a cat, Felix mightn't be my first choice. What's the Latin for "self-reliant"?