So far as I know, if two tags are "merged", it doesn't really matter which is the "original" and which is the "synonym". But even if a proposal can be made, several (4?) more users with sufficient rep (2500?) still need to vote for the change, and they all need to have at least 5 points gained from questions in (one, both, or the "original"?) tag category, so it could take a while to go through.
It's been nearly a month now, and joke/jokes are still waiting to be merged. I can't help there, because I don't have the necessary 5 points on those either.
If you've got the relevant rep, go ahead and upvote any outstanding proposals you think make sense. But be warned - many people don't like merging anything where there's any possibility of a distinction being made (once you merge, you can never regain that distinction). I don't expect style/writing-style to be merged any time soon, even though I voted for it.
I think they mean the same, but I'd keep the portmanteau-words tag.
From what I understand, portmoneau is a specific kind of blend words that are mixing words deeper than just concatenating them and potentially making one or two letters common.
A "blendword" would be a plain blend word. A "blord" would be a portmoneau. A "bearshark" is a blend word of "bear" and "shark", but a "snark" is a portmoneau of "snake" and "shark".
Not casting my vote for/against merge either way.