Self-explanatory, I hope. These both refer to the same jQuery UI plugin. They've got about an equal number of questions (nearly 1k each), but clearly having them split up like this is counterproductive.
My vote would go to making jquery-ui-autocomplete the canonical tag, since it is more inline with the 'jquery-ui-' naming scheme of other jQuery UI components.
(I still find it terribly queer that I can't just suggest these sorts of things once I hit 20k rep...I can edit the tag wikis to my heart's content but I can't suggest a simple synonym?)