I noticed that there is a tag nuance (13 uses) and nuances (117). Any one have privilege to delete tags? I think my reputation is not enough. The funny thing is in the meta site there are tag (1) and tags (19) too.
As sawa said, this situation is supposed to be handled by making one of them a tag synonym for the other. After seeing your post, I proposed to make nuances a tag synonym for nuance without considering much about the direction. After that, I learned that if someone proposes a tag synonym, the system rejects the proposal in the opposite direction automatically. So I might have messed up the situation; sorry if that is the case.
I do not have a strong opinion about which should be kept and which should be a synonym. If the consensus is to keep nuances and make nuance a synonym, I hope that moderators can rectify the situation.
In such cases, most likely someone will propose either to become a tag synonym of another. You can see the list. If you actually find it there, try to use the one that is propsed as Master. If not, you may propose a tag synonym, but probably you need certain reputation points to propose or vote.
In this particular case, nuance and nuances are not listed, so you have to think which would be consistent with other synonym pairs. I find a singular form being proposed as a synonym of a plural master, but feel it should be the other way around. Let's wait for other answers about opinions.
Note that the tag as well as the related pages work independently between the main site and the meta site.