We have questions on the synonyms for unix
One of the problems in doing anything is that there seems to be no agreement on what we should do.
Following a suggestion made in the comments of the first question I support the removal of some of these from the synonym.
Similarly for sed there are 14 questions of which 9 are directly sed syntax and two are how to install GNU sed. So in this case it might be worth keeping a sed tag but just for those.
I could also see a case for removing gnu and posix from the synonym as in AskDifferent they are not the whole system (in something like Stack Overflow POSIX does cover more e.g. programming APIs). In AD Gnu is about using gnu coreutils rather than the macOS ones.
The query for posix gives 7 questions of which I don't think any need the posix tag.
The query for gnu gives 30 many of which are re differences of GNU coreutils vs macOS ones, a few are Gnu C related and others just show GNU in an error message. I think only the former might usufully have a gnu tag - and would be better as gnu-coreutils (However would a new user know that).
In summary I think awk sed and posix should be removed from the synonym and sed added back as a separate one. This can be acted on now.
I also think gnu should be removed but less certain what to do with these questions a gnu-coreutils tag might be the answer here.