Like "Webster", the name "Roget" is in the public domain and is used by many different publishers. "Roget's 21st Century Thesaurus" is approximately the same physical size as the new fifth edition of "Roget's International Thesaurus" ["RBB" O 1 92], but--unlike the traditional classified order of that work--it employs a hybrid arrangement. The bulk of "Roget's 21st" is in dictionary order like the "Random House Thesaurus College Edition" and "Webster's New Dictionary of Synonyms", but it also has a "Concept Index" that groups together main-entry words that share the same idea or property. This index has 10 broad concepts (e.g., actions, life forms, qualities) divided into 837 more specific topics
Users of "Roget's 21st" who look up one of the 17,000 main entries in the A-Z section will find a short definition of the word, a lengthy list of alphabetically arranged undifferentiated synonyms, and cross-references to the "Concept Index," located at the back of the volume. At each numbered concept in this index, lists of related main-entry terms can be found. Users can then turn to each of these main entries to find other synonyms for the first word that have different nuances. For the user who will take the time to search each main entry referenced by the "Concept Index," this resource is a gem. For the person who wants to quickly narrow down a search for synonyms, the classified approach provided by "Roget's International" may be preferred
Although the synonyms listed in both titles necessarily overlap, each has unique words and groupings. For example, "Roget's International" provides synonyms for "ear" as a body part; "Roget's 21st" does not. Through its "Concept Index," "Roget's 21st" provides such related colorful words for the main-entry "abase" as "crucify" and "nettle"; "Roget's International" provides synonyms that fall under the general senses of "humility" and "promotion/demotion". "Roget's International" provides a list of types of guns within the synonym lists for "arms"; "Roget's 21st" does not. Both titles seem to be equally up-to-date. For example, they include such modern concepts as "significant other", such slang as "get down" and "gnarly", and such scientific terms as "genetic"
For people who want immediate access to specific words, "Roget's International" is probably going to continue as a first choice. For example, words and phrases such as "significant other", "RNA", and "all of a sudden" can be directly accessed through the alphabetical index at the back of "Roget's International"; they are not direct access points in the A-Z section of "Roget's 21st". Conversely, people who wish to browse will appreciate "Roget's 21st"'s "Concept Index," which provides access to words that may be less closely related to the original lookup. "Roget's 21st" claims approximately 38 percent more words (450,000 to "Roget's International"'s 325,000). The preface of "Roget's 21st" indicates that it uses fewer abbreviations and symbols than other recent thesauruses. Indeed, the only abbreviation used is for part of speech; an asterisk is employed to denote nonstandard usage. "Roget's International" uses 43 abbreviations to denote foreign or technical words; this information isn't found in "Roget's 21st". "Roget's 21st" provides brief definitions for all main entries; "Roget's International" occasionally provides quotations that help to define a word. Neither thesaurus provides antonyms
The preface of "Roget's 21st" states that classified editions of "Roget's" bury synonyms and that "all to often, the right word remains elusive." For those who dislike a classified approach to word finding, this may be true; for others, "Roget's 21st"'s approach may cause the pitfall that it claims to eliminate. Ultimately, a writer's first choice of a thesaurus will depend upon personal preference. But since both of these inexpensive titles are exceptional, academic and public libraries should purchase both of them. Depending upon the student body, high school librarians might also consider acquiring both.