I believe the common industry practice is to use the synonyms.txt file to list out synonyms, but this can be troublesome to maintain for sites with hundreds of thousands, or even millions of nodes in the index with a high degree of term uniqueness. Many hosting providers (acquia) also don't provide direct access to this file, and may even put a cap on the number of edits you can make.

It seems that similar functionality can be accomplished through taxonomy tagging (see ttps://docs.acquia.com/articles/using-synonyms-better-search-results). While this is currently pretty easy to implement anywhere, it is still just a pain in the butt to manage this manually when you have a high number of nodes.

I'm thinking of a system that doesn't use taxonomy, just an index field that gets filled out at index time, with a pluggable back end for swapping out "synonym generators".

Would "automatic synonym generation" be out of scope for this project? Are there better alternatives that people use?