Abstract
Thesauri and dictionaries are compatible but distinct information tools. In its 1988 edition the NASA Thesaurus [1] contains a third volume entitled “Definitions”. This practice of combining a dictionary and a thesaurus is not unique. For example “The Computer Database Thesaurus & Dictionary” [2] and “The Managements Contents Database Thesaurus & Dictionary” [3] represent fine examples of the use of both tools. Both examples present the thesaurus in one section and the dictionary in another. The “Energy Database Subject Thesaurus” [4] goes one step further by integrating definitions under some thesaurus term entries. Defined terms in the Department of Energy thesaurus are small in number, but searchers who use thesauri always find definitions useful. The Defense Technical Information Center publishes the DTIC thesaurus which is entitled “DTIC Retrieval and Indexing Terminology” [5]. It also includes some definitions with its terms. The 1988 edition of the NASA Thesaurus contains over 3,300 definitions for some 17,000 terms. These definitions at present come from three distinct sources and represent a deliberate attempt to standardize definitions. The American Society for Testing and Materials [6] has been most generous in providing permission to use standardized definitions for use with NASA Thesaurus terms. Since the NASA Thesaurus is not a commercial venture, more sources of terminology are open to it than to others. The two other sources currently used in the definitions are the “Energy Database Subject Thesaurus” and the “Dictionary of Technical Terms for Aerospace Use, NASA SP-7” [7]. In the forthcoming year, definitions from the new “IEEE Standard Dictionary of Electrical and Electronics Terms” [8] will be available in future NASA Thesaurus Supplements for appropriate NASA Thesaurus terms.