A word that has the same or similar meaning as another word is called a synonym. Synonyms are crucial in expanding vocabulary and enhancing expressive language skills. For instance, "happy" has synonyms such as "joyful," "content," and "cheerful." Understanding synonyms allows for more precise language usage and can help avoid repetition in writing and speech. The study of synonyms is an essential aspect of linguistics and vocabulary acquisition, serving to enrich communication by providing various options to convey similar ideas effectively.