What is a compound noun?

A compound noun is defined as a noun that combines two or more words to create a single noun with a specific meaning. This can include combinations of nouns, adjectives, and even verbs. For example, "toothbrush" (tooth + brush) and "mother-in-law" (mother + in + law) are both compound nouns, illustrating how distinct words can merge to represent a single concept.

In contrast, the other definitions do not fit the essence of a compound noun. One option refers to a proper noun, which is a specific name, while another describes possessive nouns, indicating ownership. The final choice relates to countable nouns, which refers to nouns that can be quantified. All of these distinctions highlight why they do not describe compound nouns, reinforcing that the key characteristic of a compound noun is its formation from multiple words to express one meaning.