KEYWORD, also key word.
1. A WORD that serves as a crucial (‘key’) element in a usage, phrase, sentence, text, subject, concept, theory, or language: Keywords: A Vocabulary of Culture and Society, by Raymond Williams (Fontana/Croom Helm, 1976), a work in the form of a glossary of such words as alienation, career, empirical, fiction, humanity, nationalist, and science, described in the introduction as ‘the record of an inquiry into a vocabulary: a shared body of words and meanings in our most general discussion, in English, of the practices and institutions which we group as culture and society’
.
2. A significant word for a person or group: ‘Self-reliance and self-care were the keywords’ ( Mary Kenny, ‘Paying the Price of Feminism’, Sunday Telegraph, 6 Nov. 1988)
.
3. A technical term for a term in a list through which it is possible to search an index, catalogue, filing system, or electronic database
.
4. Also CATCHWORD. A term in library science for a memorable or important word or term in the title, text, or abstract of an item being indexed and therefore used in the index entry
.
5. A term in cryptography for a word that is crucial in the enciphering or deciphering of a coded message.

keyword A symbol in a programming language that has a special meaning for the compiler or interpreter. For example, keywords in Basic include IF, THEN, PRINT. The keywords guide the analysis of the language, and in a simple language each keyword causes activation of a specific routine in the language processor. See also keyword parameter, reserved word.

key·word / ˈkēˌwərd/ • n. a word or concept of great significance: homes and jobs are the keywords in the campaign. ∎  a word that acts as the key to a cipher or code. ∎  an informative word used in an information retrieval system to indicate the content of a document. ∎  a significant word mentioned in an index.