The grammatical groups into which words are divided. The basic word classes are noun, verb, adjective, adverb, pronoun, preposition, interjection, conjunction, and determiners. Each word class consists of a number of sub- classes, such as proper nouns, transitive verbs, predicative adjectives, adverbs of manner, possessive pronouns, spatial prepositions, volitive interjections, subordinating conjunctions, and definite articles. Also known as 'parts of speech'.