Define "morpheme."

The concept of a "morpheme" is thoroughly defined as the smallest unit of meaning in a language. Morphemes can be entire words or parts of words, such as prefixes or suffixes, that carry semantic meaning. For instance, in the word "unhappiness," there are three morphemes: "un-" (meaning "not"), "happy" (a full word representing a state of emotion), and "-ness" (indicating a state or condition).

Understanding morphemes is crucial in the study of language acquisition because they are foundational elements that children learn to manipulate as they develop their linguistic abilities. Recognizing how these units form words and convey meanings is a key component in analyzing how children build their vocabulary and understand language structure. Other options, while related to language, do not encapsulate the essence of a morpheme, focusing instead on different aspects of linguistic units or expressions.