In linguistics content words are words such as nouns, most verbs, adjectives, and adverbs that refer to some object, action, or characteristic. Content words contrast with function words, which function primarily to express the grammatical relationships between other words in a sentence. Content words are most often open class words, meaning that new content words can be added to the lexicon easily. In relation to phonology, content words adhere to the minimal word constraint, while function words do not.