Synonyms play a crucial role in enhancing the capabilities of search systems, including Elasticsearch, by allowing different words with similar meanings to be treated equally during searches. Synonym filters can be applied at both index time and search time, each with distinct advantages and challenges. While index-time synonyms may lead to increased index size and require reindexing to update rules, search-time synonyms maintain original index size and allow for dynamic updates without reindexing. Recent improvements in Elasticsearch, particularly the introduction of the synonyms API in version 8.10, enable real-time updates of search-time analyzers, facilitating more flexible synonym management. Properly leveraging synonyms can improve search recall and relevance, but it requires careful consideration of domain-specific language and potential impacts on search scoring. The blog emphasizes the importance of ongoing experimentation and testing to maximize the benefits of synonyms while minimizing unexpected side effects.