Thanks to Peter Mark Roget the English language has a type of dictionary which is not available in many other languages: the thesaurus. A thesaurus doesn’t tell you the meaning of words, it gives you a list of words having a similar meaning to a specific word. It’s useful if you are writing a report or an essay, and wish to avoid repeating the same word several times in a short text.
The best known thesaurus is named after Roget, who published the first thesaurus in 1852. You can find Roget’s 21st Century Thesaurus online here.
You have to be a bit careful when using a thesaurus, because some of the alternatives listed may only be useful in specific situations. For example, synonyms of the word “child” include “bairn”, which is only used in the north of England or in Scotland, and “whippersnapper” which is an old-fashioned word used in the 17th century, and means “an unimportant but offensively presumptuous person, especially a young one.”