When I search for a question, It is usefull to see which tags are related to my query. How can I see related tag to search query?
I didn't see your question here before I filed a feature request for exactly this.
But then I also went ahead and wrote a user script that implements the feature.
It works on Chrome, Opera, and Firefox at least under Windows 7. I haven't tested it with other OSes.
I've now officially released this enhancement on Stackapps:
Aside: When you click Tags and then do a search, it's only searching Tag names, not tag wikis. Maybe if those descriptions were included in the search too it would help satisfy that need.
To my knowledge, clicking a tag is the only way to see related tags, which are listed in the right column, halfway down; for example, here's the tag for java on SO, and here's an example of what they look like:
Grouping Related Tags:
Search wise, the only way to manually do this is by doing a tag search using more than one tag, for example: [hello-world] + [java]