All bibliographical references are at the bottom, for those curious of mind.
The Japanese alphabets are phonetically based in such a way that they don't quite read "individual" letters, as English does. Used for the spelling of his name are katakana, the character set for "foreign" words.
Direct translation would be Shi-do-ni Ro-su-ta-ro-tsu-to, with the character "ro" rolled as to resemble "lo". Well, unless you're super manly or belting out some good ol' Shinjuku-kei rock goddess airs.
The correct pronounciation and romanization would be Sydney Losstarot. You are astounded, I know.
Commonly-- and inaccurately-- thought to have Egyptian or Hebrew origins, the word tarot is basically from the bastardization of the Italian carte da trionfi ("cards of the triumphs") or so thought.
"Around 1530 (about 100 years after the origin of the cards), the word tarocchi (singular tarocco) begins to be used to distinguish them from a new game of triumphs or trumps then being played with ordinary playing cards." Furthermore, from these very origins the saying "trump card" originates; the first actual record of this usage is in 1529, found in a sermon by English prelate Hugh Latimer. 
It's rather interesting that, once we're into the down and dirty, the name Losstarot can mean "the undoing of triumph". Chorus with me and sing "I love the smell of Pyrrhic victory in the morning!" maybe, or maybe one could think along the lines of necessary sacrifice. Was the creative team actually conscious of this decision, letting that bit slip in for little boys and girls who have far too much time on their hands? ... or some guy just thought it sounded pretty.
GUESS WE'LL NEVER KNOW. DUN DUN DUN.
Origins: there were three listed, and all of various geographical denomination. Those being French (de Sydenie or Sedeneye), Old English (multiple locations, relating to islands or lands near water) and Latin/Greek (Sidonius, or "coming from Sidon").
Another fun!fact for the day is that the "girls [sic] name Sidony derives from the Greek Sindon meaning (in honour of Christ's) linen shroud."
"The Sidney family motto is QUO FATA VOCANT which translates as Whither the Fates call."Now, that's some funky Latin going on there. And though I know all you clever people can play "Find the Vagrant Story reference!" on your own time, I'll still pick and point anyway. So, yes, one can assume that it was his "destiny" calling to take on the metal leather pants of the Müllenkamp leader, and pass it on to (a somewhat unwilling) Ashley. And taking into account Sydney's ability to discern pasts and be some self-styled prophet, this motto fits rather well.
"The use of Sidney as a first-name derives from the republican 'martyr' Algernon Sidney in the 17th century."Rather catching, as Sydney was basically the one to sacrifice limbs and the entirety of his life to setting himself up and taking the fall. As the game so lovingly details, Sydney was the one to offer salvation by setting to side those he loved, in order to bring about Ashley's ascension.
Q U E S T I O N