A week ago @JuhoKokkala raised the following Meta question: Ambiguous [combination] tag -- and the consesus was that [combination] tag should be entirely removed and replaced by [combinatorics] where necessary. (Update: This has been done by now.)
There is a conceptually related permutation tag (261 threads) which is mostly used to refer to permutation-based hypothesis tests, but sometimes refers to combinatoric problems related to permutations. I don't think this lumping is helpful.
Proposed step-by-step solution
Create permutation-test tag and tag a couple of most important related threads with it.
Go through all [permutation] threads and remove the tag from all non-permutation-test-related questions, replacing with combinatorics where necessary.
After that, merge [permutation] into [permutation-test]. (This will affect at least 150 threads, so it's better to do it automatically via the merge).
Delete the [permutation] tag as confusing (i.e. delete the synonym mapping).
Update (Feb 22): All done.