When it comes to the term "in-soluble," which means something that cannot be dissolved in water, there are several antonyms that can be used. Some of the opposite terms of in-soluble include soluble, dissolvable, or soluble in water. Another antonym for in-soluble could be hydrophilic, meaning it attracts water and can be dissolved in it. Alternatively, something that is "miscible" with water means that it can dissolve in water to form a homogeneous mixture. In summary, the antonyms of in-soluble are all words that relate to the ability of a substance to dissolve in water.