Semantic change refers to the evolution of word meanings over time. This process can occur in various ways, such as broadening, where a word's meaning expands to include more concepts, or narrowing, where it becomes more specific. For example, the word dog once referred to a specific breed but now encompasses all canine species. Another type of semantic change is amelioration, where a word takes on a more positive meaning, and pejoration, where it acquires a negative connotation. An example of amelioration is the word knight, which originally meant "servant" but evolved to signify a noble warrior.