A dictionary is a reference book that contains an alphabetical list of words, usually with their definitions, pronunciations, and etymologies. It also often includes usage notes and examples of the words in use. A dictionary is an invaluable tool for language learners as it can provide insight into the meaning and usage of words, as well as helping to expand vocabulary. Additionally, it can provide a source of entertainment when looking up obscure or interesting words. Dictionaries are typically organized into entries which contain information about each word. The entry may include the word’s pronunciation, its definition or definitions if there are multiple meanings, its part of speech (noun, verb etc.), its etymology (the study of the origin and development of a word), its related forms (other words related to it such as synonyms or antonyms), and any other information regarding its usage in context. Most dictionaries also contain accompanying images or illustrations that provide additional context for understanding how to use the word in question. Additionally, some dictionaries will list collocations (words commonly used together) for each entry so that learners can see how different words are used in combination with one another. Finally, many dictionaries will also include a section on grammar rules and usage notes to help explain why certain forms are correct while others are incorrect. This section is particularly useful for those learning a new language who might not yet be familiar with all the rules governing how to form sentences correctly.