According to What are tag synonyms and merged tags? How do they work?
All good tag synonyms should eventually be merged.
Currently, we have 60 non-merged, and stable synonyms (see EvilGenius's comment why not 61). Stable in the sense more than two months working as synonyms and without complaints.
This is a Q/A in Cross Validated Meta (which I participated) that elaborates on why the community there decided to merge all synonyms in the main site (and also in meta).
Is there anything preventing us for merging tag synonyms here in GIS SE?