(There are some
writeups on
E2 under the impression that words mean what someone with claims to the right of definition defines them to mean. In
linguistics, the assumption is rather that words mean whatever users of those words mean when they use them. So it seems appropriate to do another writeup here, this time from a linguistics point of view.)
Whatever Sun marketing likes to say, most users of operating systems manufactured by Sun Microsystems tend to use SunOS to refer to the version of Sun's OS up to SunOS 4.x, while Solaris is used to refer to everything that came after it.
There is a clear explanation for this: the "Solaris" term and the SunOS 5.x OS were introduced at the same time, so it was only natural for users to identify the two. The original idea, which, as semprini writes, was to reserve the term "SunOS" for the OS kernel and introduce "Solaris" as a name for the whole package, just didn't catch on.
A whole lot of stuff and users already referred to "SunOS" as the old system, whether it was just the kernel or the whole package; meanwhile, Sun kept promoting the use of the new term by consistently referring to the new OS as "Solaris 2". The fact that they also referred to the new kernel as "SunOS 5", and to the old system as "Solaris 1", was lost on everybody.
And with good reason. You can introduce new names for new things, but to introduce new naming for existing things really requires some strongly compelling arguments. And Sun didn't have any. Users felt little need to distinguish the kernel from the whole package by separate names; but they did need a new name for the new system. After all, Solaris (sorry I can't help it) was an entirely different flavour of Unix, with entirely different performance characteristics, and initially, a lot of severe incompatibility issues, most of which were addressed by Sun as the system matured. It's simply too confusing to refer to such a drastic change only by an increased version number, as Sun would have liked users to do.
Another case to prove that there's only so much you can do with word bending and creative marketing. See Unix for another example.