The term "most castoff" refers to something that is frequently discarded or abandoned. Its antonyms are words that indicate something is highly valued, cherished, and kept with utmost care. Examples of antonyms for "most castoff" include precious, invaluable, treasured, prized, esteemed, and esteemed. These words convey a sense of high regard and worth, which stand in stark contrast to the negative connotations of "most castoff." Thus, when we use these words to refer to something, we are highlighting its significance and highlighting our desire to keep it with us.