Tomarin: You have to study the rudements of the Gaelic, Celtic, language origins. Authorititave, that’s a good question. Both languages have been influenced by Norse, Saxon, and many words of the Celtic Gaelic language have been assimilated into the Norman/Saxon middle age English. Fitz is one of those words. If you read Wikipedia, it will tell you that Fitz was reserved for illegimate sons of royalty, not quite true, just a point in time. The word “fils” comes from the Latin word “Filus” meaning “son”. Many mistake that for the origin of Fitz. Not true. As I said before, those bronze age people that followed the animals and fowls across the land bridge had a rudimentary language, which after many thousands of years became Celtic, Gaelic, Welsh, etc. While some words are the same in all three languages, many are different as dialects turn into another language form by distance and time. That’s the way I learned from my professors. I’ve studied what is called modern Celtic and Gaelic and found both to be very hard to use as both are very gutteral and hard to sound, much like an oriental trying to say “L” in English pronounciation. My avatar Sinnseanair means great grandfather in Gaelic. Please do not ask the conjugation, I am not that well versed. The word structure of these languages have correlation, but unlike Latin it is not strict such as filius, “us” always meaning masculine and fili, “i” meaning singualr possessive as in “In nomeni Patri, et Fili, et Spiritu Sancti” You must also remember that today’s version of Gaelic and Celtic are but memories since these languages were forbidden to be spoken by conquering nations for a number of years. So, the word fitz originally came from Gaelic, assimilated into middle English and on to today’s phonebooks. Originally it meant to label a man’s son born out of wedlock, to connote the law of primogeniture or the law of the oldest son inheriting the father’s wealth, farm, fields, cattle, etc. and one born out of wedlock was unable to fall under that law. The primogeniture law is one of the oldest sustained laws of many cultures. So, if you were named John and married and that marriage produced a son, his name became John’s son or today’s Johnson in English. If John happened to mess around and produce an illegimate son, that was FitzJohn or the bastard child of John. John’s son inherited all of John’s holdings while FitzJohn or today’s Fitzjohn got nothing. Most Celtic Gaelic men had only first names for centuries until there became clans of extended families. “Mac” in Celtic mean literally "of the clan of, not the son of. O’ stems from the famous Irishman Brian Bararu, a king of Ireland whose family after he was killed called themselves “Of Brian” or today’s O’Brian. That is how most Celtic and Gaelic surnames names were founded and traced. In Gaelic, since I am a grandfather I would be called “seanair”. As a great grandfather, I am called “sinnseanair”. Much like Grandfather or in the Southern United States Grannpaw, and Great Grannpaw. The superlative added to connote generation. You must remember that the Celtic and Gaelic dialects that became languages are far older that a Norman Saxon mixture which became middle english, a forerunner to today’s modern english and about 70 or so percent of American English. There may a small correlation between the ancient peoples that became the Normans and the ancient peoples that became the Celts and Gaels in that both have common ancestors in a rudimentary language used by the people of the bronze age to include those who left to follow the food across the land bridge between what is now France, England and Ireland becoming cut off when the melting waters of the Ice Age that overflowed that land bridge making today’s English Channel and Irish Sea. If you want absolute truth, you’re going to study the origins of these languages as I did many years ago. There are more twists and turns than there are myths retold often enough to make them sound true. Good Luck and God Bless.