Retting is a process of soaking materials such as flax or hemp in water, allowing them to ferment and rot, and separating the fibers from the woody material. However, if you're seeking synonyms for retted, you'd find a limited number of options. A few possible terms that might bring a similar meaning include softened, decomposed, and degraded, but they do not specifically indicate soaked in water. These synonyms may apply to natural or artificial means, such as chemical processing. However, retted remains the most appropriate word to describe this specific method of fiber extraction.