Arched over is a phrase typically used to describe a concave shape or a structure that is curved, bent or bowed. The antonyms for the word "arched over" would be descriptors for a structure that is straight, flat, or upright. Words like "level," "straight," "horizontal," and "uncurved" would be antonyms. An "arched over" structure tends to create a sense of enclosure, whereas its antonyms can create a sense of spaciousness and openness. The choice of word depends on the context and the intended meaning. In general, it is important to consider the antonyms of a word to understand it better and to avoid misinterpretation of the intended meaning.