There are several antonyms for the word "echinated," which means covered in spines or prickles. The first antonym is smooth or unspiny, meaning having a surface that is even and without any protrusions. Another antonym is soft, indicating that the surface is gentle and not sharp to the touch. Additionally, flat can also be used as an antonym for echinated, implying that the surface is level and even. Similarly, sleek and streamlined can be used to describe a surface that is smooth and without any sharp edges. Finally, rounded or curvy can also be used as antonyms, indicating a lack of sharpness or angularity on the surface.