Not sure how this one slipped through... again.
I say do it. Wikipedia considers them the same thing and as far as I know, they are.
However, there might be a bit of confusion for any Java developers and that might be a drawback. Apparently both exists as separate entities, so we'll need to be prepared to explain that tags such as these are not language specific.
Yes, let's merge these - probably into hash-map, as that's the one with most questions (by only a small margin).
I've copied the useful stuff from hash-table into it in readiness for the merge.
Definitely yes to the synonym once it's done.
(I don't understand why this question is status-completed; did it somehow get discompleted in the intervening years?)