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I you are going to search for books by Subject, how can you know if they will be indexed under the common term, "heart attack," or the clinical term, "myocardial infarction"? Under "high blood pressure" or "hypertension"? By using the Library of Congress Subject Headings thesaurus.
Will help if you need some related terms to your main search term; use this database to find subject heading terms used in the library catalog.
Subject headings are a controlled vocabulary of subject terms, or "headings," that are used to take the guesswork out of subject searching by assigning a single term to describe a topic. For example books about the death penalty or a death sentence would be indexed under the subject heading "Capital punishment."
"Library of Congress Subject Headings (LCSH) has been actively maintained since 1898 to catalog materials held at the Library of Congress. By virtue of cooperative cataloging other libraries around the United States also use LCSH to provide subject access to their collections. In addition LCSH is used internationally, often in translation. LCSH in this service includes all Library of Congress Subject Headings, free-floating subdivisions (topical and form), Genre/Form headings, Children's (AC) headings, and validation strings* for which authority records have been created. The content includes a few name headings (personal and corporate), such as William Shakespeare, Jesus Christ, and Harvard University, and geographic headings that are added to LCSH as they are needed to establish subdivisions, provide a pattern for subdivision practice, or provide reference structure for other terms. This content is expanded beyond the print issue of LCSH (the "red books") with inclusion of validation strings."