Synonym mapping for classification lookup / classifying documents

We maintain a YAML file containing both the stemmed and the unstemmed version of the words. Look at how we handle business/businesses here:

The actual ES synonym file we generate from this YAML contains this entry:

business, businesse

If you have a synonym filter after your stemmer, you will need to put the stemmed form in the synonyms file. Otherwise you have to list out all the possible word forms.