A monolingual dictionary is a reference book that provides definitions and explanations of words in a single language. It helps users understand the meaning, usage, and pronunciation of words without translating them into another language. These dictionaries often include examples, synonyms, and grammatical information to enhance comprehension. Monolingual dictionaries are commonly used by language learners, writers, and researchers to improve their vocabulary and language skills. They can vary in size and complexity, ranging from simple dictionaries for children to comprehensive ones for advanced users. Popular examples include the Merriam-Webster Dictionary and the Oxford English Dictionary.