Arch over means to form or make into an arch shape over something. The antonyms for this word would be to flatten, level or straighten. These antonyms imply the opposite of forming a dome or bending over something. When we think of arching over, we might imagine a bridge or archway, but by using the antonyms above, we can think of a flat, even surface or a clear pathway. Using antonyms in our writing and speech can add variety and depth to our communication.