Databases usually utilize a controlled vocabulary or a thesaurus, which includes e.g. the terminology of a certain discipline. Controlled vocabularies usually apply to a particular database, but they can also be universal, independent of databases and subject areas.
Articles in databases are described with subject terms, which can be used both in choosing your search terms as well as in information retrieval.
Many thesauri describe the relationships between words (broader, narrower and parallel terms). If there are too few references, it is worthwhile to try a search with broader terms. If there are too many references, you can use a narrower term. Note that a parallel term is not the same as a synonym. Controlled vocabularies may also show what subject term is used for the concept in stead of the term written by the searcher.
When you have chosen your search terms from the thesaurus of the database you can conduct your search with these words and direct your search into subject term fields.
First search for results with the search words you know. For example in Scopus you can find more potential search words with the tool "Refine results" under "Keywords".
Finnish thesaurus and ontology service is a universal vocabulary independent of databases and subject areas.
Image source: General Finnish vocabulary <https://finto.fi/ysa/en/?clang=fi> 28.12.2018
In the thesaurus for the central database for the Faculty of Education, Eric (ProQuest), one can see that in stead of the term left handed writer the term handedness is used. Image source: ProQuest <http://search.proquest.com> 14.7.2017
Free search terms vs. controlled keywords