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Stage 1 of 3
thēsauros
Greek · ancient
"treasure, storehouse"
Greek, the root of 'treasure'
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Stage 2 of 3
thesaurus
Latin · ancient
"treasury"
Roman writers used it for a treasury or storehouse
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Stage 3 of 3
thesaurus
English · 1820s
"dictionary"
Roget's Thesaurus of 1852 fixed the sense 'book of synonyms'
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