Rated 5 out of 5 stars
Better than excellent.
Dictionary Tooltip is by far the most ergonomic, click conserving, and well designed dictionary aid; all others have been uninstalled. The ability to add any custom dictionary via a small script is icing on the cake, as are numerous small nice things. It was worth a donation before, and is even better now; upgrade was seamless for me.
Using Stylish, the results of a word search can be 'cleaned up' to only display relevant content and thus a smaller tooltip.