"clobber" is commonly used to mean "overwrite". This has been true for over a decade (csh has had a "noclobber" option for more than 10 years).

Now "clobber a predefined variable" can be made more precise as "clobber a predefined variable's value". In the original(?) use of the term, it was a file that was being overwritten, which makes the distinction even less problematic since the clobbering of the file's contents was often accomplished by overwriting the file with a different file (now with the same name that the original file used to have) rather than by keeping the same file and just overwriting the contents of that file (but both were possible and the distinction was rarely important since the point was that your file's original data was no longer available via the original file name).

So I find it natural to interpret "clobber a predefined variable" as "clobber a predefined variable's value" in the absence of any evidence that we are actually talking about the less-common act of removing variables from symbol tables or replacing them.

"Clutter" certainly doesn't fit this case, as Jenda explains.

                - tye