When the word anomaly was first borrowed into English in the 1570s, it meant something more like "unevenness" than its modern definition, but it was an easy extension from there to a connotation of "deviation from the ordinary" that developed in the 1660s. Before then, the word came from Latin anomalia, which came from Greek anomalos, which essentially had the same meaning. Here it gets interesting as we break apart anomalos into two: the prefix an- means "not" and the root homalos means "even", so an anomaly is, etymologically, "uneven". Homalos is from homos, meaning "same" (and the same root as can be found in words like homosexual and homogenous), which derives from the Proto-Indo-European reconstruction sem, which could mean "one" or "together". Quite interesting!
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
The Etymology Nerd