The synonym rule allows you to specify if you want to give synonym more importance than the original word when ranking search results. For example, assume the webpages of your site that contain the word 'New York City' are more important than the pages that only contains the word ‘NYC’. When creating a synonym, choose "More" option from the dropdown to make results for 'New York City' more important than results for ‘NYC’. It will then rank the pages that include the word 'New York City' higher for results where the scores were equal.