The antonyms of the term "sub division" can be either "merge" or "combine." When we merge things, we bring them together to form a unitary entity. Similarly, when we combine things, we join them to create a single, unified whole. Opposite to sub division, these two antonyms stand for the process of adding up or bringing things closer to each other. For instance, a company can merge with another company to create one bigger company. Similarly, two small pieces of land can be combined to form a larger plot. Therefore, sub division is the process of dividing something when merge or combine is the process of uniting things.