The phrase "is erect" refers to something that is standing straight up or firmly in a vertical position. Its antonyms would include words like "is slouching," "is lying down," "is leaning," "is drooping," or "is sagging." These words describe the opposite position or stance of "is erect." For example, when we say someone is slouching, we are describing someone who is not sitting or standing up straight. Similarly, when we say something is sagging, we are referring to something that is not held up or supported properly, and therefore, is hanging down. These words offer a range of alternative meanings to the term "is erect.