Library catalogs and article databases, use special terminology lists for describing items in their collections. Most academic libraries and many public libraries use the Library of Congress Subject Headings.
The terms used may differ from common language. You might phrase a keyword search for your topic as "American Revolution." That phrase might be in the title or the summary of a book but if the phrase "Revolutionary War" appeared instead, you would fail to locate the book. It is best to use the terminology that the system uses consistently to describe a subject. For example, there's an LC Subject heading "United States History Revolution 1775 1783" that would be assigned to all books related to that topic.
LCSH (Library Of Congress Subject Headings) - use with most library catalogs and some general databases, such as Academic Search (EBSCO).
Some periodicals databases list their subject headings in a Thesaurus usually linked from the menu bar above the search screen.