Edit: Synonyms in Stackoverflow seem to be two-way. That is, i now think se should not add this synonym anymore. Because making STL synonymous with standard-library is just plain wrong. What I meant in my original post is a one-way relation: Make questions tagged by STL being retagged to standard-library, but making standard-library not synonymous with STL (because it isn't!).
I see now that synonyms are not the proper tool for this.
"stl" is used as a tag by people asking about stuff in C++'s standard library components, like std::vector and so on. Stuff that used to be in the STL library back in old days and hence sticks to that name since today.
Nowadays, it's increasingly clear that people intend to refer to the standard library if they tag their questions by "stl". Especially in the light of the upcoming C++0x's components. Does c++0x's std::array belong to STL just because it's a "template component" or to c++-standard-library? Or to both? To clear up matters, I propose to add "stl" as a synonym to "c++-standard-library" (I have already created a synonym to add that in turn as one to "standard-library").
It could be worth-while to add "standard-library" in turn as a synonym to "stdlib", since the latter is shorter and also proposed currently by the "stl" tag info. I don't know about that, although I feel that the latter is shorter and commonly used.
To specifically refer to the original STL specific things, people could use "sgi-stl".