A while-ish ago, I suggested a tag synonym here. After this while-ish, it's still stayed at 0 votes. While this could mean that its upvotes and downvotes canceled out, I really doubt that because it seems unlikely, given what the actual synonym is. First of all, I want to know how long it takes before someone actually votes on it. Second of all, please vote on it!
Tag synonym suggestions are largely ignored unless specifically raised.
There's no easy way to navigate to the tag synonyms page, and I'd guess very few if any people regularly check for tag synonym suggestions. Also the system won't automatically bring any proposed tag synonym to the attention of users able to review it (e.g. there's no review queue for tag synonym suggestions). So if you just propose a synonym and let it lie, it's very unlikely to be seen. You could ask for help in chat, or better on meta, to get a tag synonym approved.
It's often useful to get moderator help for tag synonymisation. The merge tool (only available to diamond mods) is usually better to use than the synonymisation tool, since it leaves no trace of the synonym tag hanging around on old questions even though it can't be added to new ones. For very clear cases you might consider raising a mod flag, but apparently it's possible that someone might consider two tags "clearly synonymous" which actually aren't at all. That brings me to the second point ...
Your particular suggestion was very wrong and has been rejected.
It's no longer visible on the page you linked to in the OP, but from comments and the other answer here I gather that you proposed novel as a synonym of books or vice versa. As has already been explained to you in comments, these two are not remotely synonymous, either as tags on SFF.SE or even as English language words. Many books are not novels, so the words are not the same, and for our site it's useful to break down the general books tag into subcategories like novel and short-stories with their own tags. So the community rightly downvoted your tag synonym suggestion enough that it disappeared.
Tag synonyms take an indeterminate amount of time to be voted on due to how they work. As far as I know there is no automatic system that notifies anyone to vote on a tag synonym request. People need to visit the tag page or Tag Synonym Dashboard.
Then that user needs an answer score for that tag of at least 5:
Users with a total answer score of 5 or more on the tag, can vote for tag synonyms.
The best way to speed up the process is to either ask a meta question on it, preferably beforehand asking if it is a good idea, ask in chat or flag for moderator attention. I would use the last option sparingly though and where it is essentially a clear cut case.
A note about this request
This request should get declined as the tags have different uses. Just in regards to story-identification questions novel is used when trying to identify a novel and books is used when identifying a series or when we don't know what sub type of book it is i.e. they say book but don't specify between novel, novella, short story, etc.