Stelliform is an adjective that means star-shaped, and it is often used in the realm of astronomy to describe celestial bodies that resemble stars in shape. Antonyms for stelliform include forms like circular, square, triangular or any other shape that is not star-shaped. These words describe shapes with regular contours or lines that do not branch out in the same way as stelliform shapes. One might also use amorphous, shapeless, or nebulous as antonyms for stelliform, which refer to shapes without any specific form or structure. Stelliform is a specialized term, but it can be useful in describing stars, galaxies, or even certain crystals.