A reference book that groups words by meaning, similar to a synonym dictionary. Often used in writing and language study.
When I write, I consult a thesaurus to find expressions.
シソーラス is a loanword from English and often used in computational or academic contexts, while 類語辞書 is the native Japanese term and more common in everyday reference to a printed or digital thesaurus.
類語辞典 is a near-synonym; both refer to a thesaurus. 類語辞書 may slightly emphasize a dictionary-like reference, but in practice they are interchangeable.
Compound of 類語 (ruigo, 'synonym') and 辞書 (jisho, 'dictionary'). The exact historical derivation is uncertain, but the term follows standard Sino-Japanese word formation.