The antonyms for "more frontier" can be "settled," "developed," or "civilized." These words refer to areas that have been inhabited, cultivated, or urbanized. They suggest a lack of wilderness, a lower intensity of natural resources, and a more stable social and economic structure. In contrast, "more frontier" indicates unknown, untouched, or untapped territories, where risks, challenges, and opportunities abound. It implies a sense of adventure, exploration, and expansion. However, the idea of "frontier" can also evoke the negative aspects of colonization, imperialism, and exploitation of native populations and environments. Therefore, the antonyms of "more frontier" may represent a more sustainable and respectful approach to the land and its inhabitants.