GS4ME, Giuigiaro is pronounced "Jew- JAR- o". Original GS based on GG's show car, the Kensingtion, which was a design he pitched to Jaguar as a possible 4 door sedan to replace the old XJ6. Obviously, Jag wasn't interested and Toyota/Lexus was. The current GS was done in house.
So far, we appear to have good explanations for all acronyms except IS. Intelligent Sedan? (nope) Idiot Sedan? (don't think so) Intense Sled? (doubtful) Internally Satisfying? (let's not forget the Japanese have some very strange vehicle names when the original Japanese monikers are faithfully translated, but I think this one still ain't it) Further speculation will be left as an exercise for the reader......
In the gloom and darkness of the night, when there is a sudden flash of light, a person will recognize objects; in the same way, the one with a flash of insight sees according to reality--"This is how sorrow works; this is how it arises; this is how it can come to an end; this is the path leading to that end."