Compare this to a dictionary which lists words alphabetically and then gives their meanings.
A typical dictionary might show the word, it’s word class and then an explanation:
teacher noun someone whose job is to teach, especially in a school.
teacher noun schoolteacher, educator, guide
Kinds of teacher include: adviser, coach, college lecturer, counsellor, crammer, dean, demonstrator, deputy head, doctor, don, duenna, fellow, form teacher, governess, guru, head of department, head of year, headmaster, headmistress, headteacher, housemaster, housemistress, instructor, lecturer, maharishi, master, mentor, middle school teacher, mistress, nursery school teacher, pastoral head, pedagogue, pedant, preceptor, preceptress, primary school teacher, principal, private tutor, professor, pundit, reception teacher, school-ma’am, schoolmaster, schoolmistress, schoolteacher, secondary school teacher, senior lecturer, student teacher, subject co-ordinator, supply teacher, trainer, tutor, university lecturer, upper school teacher.
Both examples above were taken from the online Chambers dictionary.
Unlike a dictionary in which words are listed alphabetically, Roget’s is grouped by concept starting with abstract concepts such as existence and state and then moving on to quantity, order and suchlike and to action, volition and belief.
The word thesaurus comes originally from the Greek θησαυρός literally meaning treasure store, which generally meant a store of valuable items. Today the word is used almost exclusively to describe the book.