The antonyms for the word "more newborn" include "older," "mature," and "fully grown." These opposites imply that the subject has progressed beyond its initial stage of development, and has acquired greater knowledge, experience or physical growth. Additionally, other antonyms for "more newborn" can include: "adult," "senior," "veteran," "ancient," and "aged," each of which suggests a greater degree of wisdom or experience gained through time. Understanding these antonyms can help individuals better conceptualize the life cycle of living beings and the varying stages of development that take place over time.