The Zombie Stack Exchanges That Just Won't Die
As of this writing, interlibrary has 2 questions (one tagged both interlibrary and loan) and interlibrary-loan has 2. Obviously these are intended to be the same category, so I've submitted retagging edits for the two [interlibrary] questions. However, this may not be sufficient to indicate a need for a synonym, and people may wish to disagree with my preference for [interlibrary-loan] over [interlibrary].
I believe that this does indicate a need for a synonym, as clearly we are experiencing splintering in the tag structure and the full name of interlibrary loan is more understandable to people who don't deal with the subject regularly (and therefore might have questions about it) and will show up when people do searches for the full phrase. Furthermore, one of the prior [interlibrary] questions appears to have been by someone who simply didn't understand how to make multi-word tags, as it was tagged [interlibrary][loan].
Since the questions have been retagged, interlibrary doesn't exist anymore. If someone goes to type it in when posting a question, interlibrary-loan will come up as a suggestion, so I think the odds of it reoccurring are relatively small.
In order for me to create a synonym, I'd have to recreate the tag, which seems a little silly at this point. :)
If it does come up again, we'll revisit setting up a synonym.