Looking through the pages of tags I noticed many that are the same. An example are the tags usaf and us-air-force. At this point nobody has made a synonym for them. I was surprised to find that I can't even suggest a synonym since I don't have 5 up-votes in the tag (and likely never will). I can see having to have activity in that tag to vote on a synonym but if you notice one that needs a synonym you should at least be able to suggest it.
The general idea is that if you don't have at least 5 up-votes in a tag you probably don't have enough domain-specific knowledge to be suggesting synonyms. A good question (or answer) can easily garner the 5 upvotes required to meet this threshold.
Of course this leads to edge cases like this one, where it's pretty obvious a synonym should exist but nobody with the necessary upvotes has though of suggesting it yet. For these cases (or really any blatantly-obvious cases) the thing to do is open a Meta post, and usually a moderator will come along and merge the tags. This is also usually faster than the user-driven synonym process.
In this case I've merged usaf into us-air-force, in part because the latter had a more complete tag wiki entry. usaf will remain as a synonym (the expanded form will show up in tag lists, but the short form can be used in searching and adding tags).
5$\begingroup$ Note that this is the case on essentially every site, including SO. $\endgroup$ Jan 26, 2016 at 22:09