To create a tag synonym:
Click on a tag, any tag, anywhere you see it displayed on the site.
Click on the "synonyms" link.

Enter the name of the tag you want to propose as a synonym in the text box, and click "Suggest".

Note that there are certain requirements for proposing a tag synonym, documented in the tag synonyms page. Specifically, to suggest tag synonyms, you must:
- Have more than 2500 total reputation.
- Have a total answer score of 5 or more on the master tag for which you are proposing the synonym.
If you don't meet the reputation requirements to propose a tag synonym but feel very strongly about the merit of your suggestion, then please post a new question here on Meta, and tag it with the discussion and tag-synonyms tags. This allows the community to discuss your proposal, and if agreed upon, it can be implemented by several users with sufficient reputation or a moderator.