Data Dictionaries and Thesauri
Data Dictionaries contain structured data names, and thesauri contain terms that make your data more easily discovered.
Definition: Data Dictionary
According to the DOI Data Management Guide [PDF] (2008), a data dictionary is a repository of data (metadata) defining and describing the data resource.
A thesaurus is a structured list of preferred terms or subjects that indicate relationships between those terms. Preferred terms are focal points where all information about a concept is collected. Relationships between preferred terms can be broad, narrow, or related in another way.
A thesaurus also indicates non-preferred terms, which are terms indexers and searchers should not use. A good thesaurus makes clear what a term is meant to cover by providing preferred terms, their relationships with other preferred terms, and non-preferred terms.
Data Dictionary Definitions
Entity: Fish Measurements - A sample of the physical measurements of rainbow trout in Lake Superior, MN collected on 07/14/2010.
Data element (attribute) definitions:
Example USGS Data Dictionaries