Etymologically speaking, when you refer to your "maternal uncle" you are really saying my "mother's mother's brother" or even "mother's grandfather". Uncle comes from French and the curiously spelled word oncle, which traces further back to Latin. Here it was avunculus, which only referred to what we today call a maternal uncle. This is also the direct root of the word avuncular, which means "of, or relating to, an uncle". This is a conjugated form of the word avus, which meant "grandfather". This, like much of Latin, goes back to Proto-Indo-European, in this case to the word awo, meaning "grandfather". Going further back, this reconstructed word meant "any non-paternal relative". As a native Serbian speaker, I know Serbs say ujak for uncle, and I was unsurprised to learn that this too traces back to awo. Similarly, I was tickled about the change in generation, from "grandpa" to "uncle". Maybe someday "uncle" will mean "nephew"!
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd