The best way is, in my experience, let the users tag away. Then add the tags to the item descriptions in the full text search (while also holding on to the norm

The best way is, in my experience, let the users tag away. Then add the tags to the item descriptions in the full text search (while also holding on to the normalized data, because refactoring tags is a thing). If your FTS system allows the definition of synonyms, even better. Users get the usual autocomplete, and suggested tags. Searchers get approximation. I never implemented this before but the tags can also hold references to the tags they are most frequently tagged with to further add content to the depleted search results. Never thought how the implementation would look like though.