Synonyms are different words with similar or almost identical meanings, e.g. teenagers, adolescents or young people all mean the same. Using synonyms is crucial for comprehensive literature searching because, different authors may use varying terminology to describe the same concept. By including synonyms in your search, you increase the chances of retrieving all relevant articles on the topic. For example, if searching for "drug addiction", you should also include synonyms like "substance abuse", "narcotics", "heroin use", etc. to find articles that use alternative phrasing.
Synonyms account for variations in word forms and spellings. Including singular/plural forms (e.g. addict/addicts), alternate spellings (e.g. tumor/tumour), and related terms (e.g. addiction/addicted) ensures a more exhaustive search. Controlled vocabulary databases use specific indexing terms which may differ from common keywords. Searching for relevant subject headings/thesaurus terms in addition to keywords maximizes retrieval of indexed articles on the concept. Identifying all relevant synonyms helps avoid missing potentially important literature simply due to an author's choice of wording. The optimization technique of comparing keyword and thesaurus term results can uncover additional synonyms to include. In summary, using a comprehensive set of synonyms, spelling variants, controlled vocabulary terms, and related phrases is essential for a complete and unbiased literature search on any topic. Omitting synonyms risks overlooking relevant articles, leading to an incomplete review of prior research.
Read more about how to utilize synonyms in databases by reading the Boolean Search Operators page in this how-to guide on literature searching.