Spongy is defined as something soft, compressible, and yielding under pressure. Therefore, antonyms for spongiest would mean words that convey a completely opposite meaning. Some of the antonyms for spongiest are hard, firm, unyielding, solid, non-absorbent, and stiff. Words like rigid, compact, impermeable, and unyielding can also be used as antonyms for spongiest. These words are used to describe objects, textures, or surfaces that are opposite in properties to spongy materials. In summary, spongy has characterized objects that are absorbent, yielding, and soft. Conversely, antonyms for spongiest are harder, rugged, stiff, and non-absorbent objects.