Synonyms
'Thesaurus' means treasure house
Greek thesauros described a treasury. Roget chose it deliberately, framing words as riches to draw from.
More in Synonyms
'Big', 'large' and 'immense' are not equal
Synonyms rarely mean exactly the same thing. Register, intensity and connotation shift, which is why writers choose carefully.
'Ask' and 'inquire' change your tone
Anglo-Saxon words feel plain and warm, Latin-derived synonyms feel formal. English lets you switch registers instantly.
English has three words for almost everything
Invasions left English with Anglo-Saxon, French and Latin layers, so we get kingly, royal and regal for one idea.