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 subclasses, 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'.