The word "un-worldliest" can be defined as lacking experience or sophistication in worldly affairs. Its antonyms would be words that convey the opposite sense, such as cosmopolitan, worldly, or sophisticated. Someone who is cosmopolitan has a broad knowledge and experience of different cultures and ways of life, and is well-travelled. A worldly individual is knowledgeable about life and its ways, and is not naive about human behavior or cultural norms. Similarly, a sophisticated person has a refined taste, is cultured, and has acquired social skills and worldliness through their experiences. All these terms suggest a person who is worldly-wise, cultured, and sophisticated - qualities that are the opposite of being un-worldly.