We currently have five questions about the the Lamport one-time signature scheme tagged with lamport-signature. Every single one of them is also tagged with hash-signature. While the tags differ somewhat in scope (there are other hash-based signature schemes besides Lamport's original one, although AFAIK they're all more or less directly based on it), I don't believe there's really enough difference to support two separate tags.
I could just edit the lamport-signature tag out of all the questions (like I just did for the single-question tag one-time-signature), but it would be nice to see it retained as a synonym, so that someone typing "lamport" into the tag field would get useful suggestions. I don't have the tag weight to even suggest the synonym, though, much less get it approved (do we actually have any tag synonyms approved through community voting yet?), hence this meta post.