Here is a really simple way to handle synonyms (or extra keywords) using Search API out of the box with a database server and no custom code involved. Use case: we want to do a full text search based on synonyms that does not appear on the frontend. These ones should be set from the Tags vocabulary. The method should be flexible regarding translations, available for content editors and easily generalizable.
CiviCRM is an old Drupal 7 friend and its relationships with Drupal 8 are in a pretty good way. Let's make them meet the Composer template for Drupal projects, a widespread setup that stores the vendor directory outside of the docroot. Lando will host the party by spinning up a local environment, however this method should be generalizable with any other development environment.