While Jill was looking up synonyms in the thesaurus, she also consulted a new dictionary which was helpful in that it had a special glossary of specialized words which she had not seen when she reviewed the old lexicon that her friend had given to her.
2. A dictionary of words relating to a particular subject.
3. A place in which valuable things are stored.
4. Etymology: from 1823, "treasury, storehouse"; from Latin thesaurus "treasury, treasure"; from Greek thesauros, "a treasure, treasury, storehouse, chest"; from root of tithenai "to put, to place".
The meaning "encyclopedia filled with information" is from 1840, but it existed earlier as thesaurarie (1592), used as a title by early dictionary compilers. The meaning, "collection of words arranged according to sense" is first attested 1852 in Roget's title. Thesaur is attested in Middle English with the meaning, "treasure" (about 15th century-16th century).