In the end a feature will just be a numerical value. How do you plan to use synonyms in a field to generate a numerical feature ?
Are you planning to define a binary feature for a field, in case there is a match on the synonyms ? Or a feature which contains a score for a query ( with synonyms expansion) ? I would start from the SolrFeature, let's assume the "title" field has a field type that includes synonyms ( query time) : { "store" : "featureStore", "name" : "hasTitleMatch", "class" : "org.apache.solr.ltr.feature.SolrFeature", "params" : { "fq": [ "{!field f=title}${query}" ] } Query time analysis will be applied and synonyms expanded. So the feature will have a value , which is the score returned for the query and the document ( under scoring) . You can play with that and design the feature that best fit your idea. Regards ----- --------------- Alessandro Benedetti Search Consultant, R&D Software Engineer, Director Sease Ltd. - www.sease.io -- Sent from: http://lucene.472066.n3.nabble.com/Solr-User-f472068.html