You can enable synonyms words to search on your site to make the searches find better results.
To enable synonyms words search, just add synonyms words in the Synonyms plugin option displayed in the plugin settings page as shown below. The format is key = value such as bird = crow and please separate every synonym key = value pairs with a new line.
If you add bird = crow to the list of synonyms, searches for bird automatically become a search for bird crow and will thus match to posts that include either bird or crow.
Please note that this synonym only works for search forms configured for searching any of the searched terms or we can say having OR relation in the searched terms. If the search form is configured to search all the searched terms or has AND relation then the synonyms only restrict the search, as now the search only finds posts that contain both bird and crow.