The word "most gossamery" means extremely delicate or light. Its antonyms would be words that express heaviness, density, or solidness. These could include, but are not limited to, sturdy, substantial, heavy, thick, solid, robust, weighty, dense, or significant. These antonyms describe things that are strong and durable, rather than fragile or easily broken. Alternatively, antonyms may focus on the opposite of lightness, such as darkness, obscurity, or opacity. Nonetheless, most commonly used antonyms for the word "most gossamery" tend to express the opposite of delicacy and lightweight.