There are several antonyms for the phrase "most erosive." These words would describe substances or materials that are gentle, non-abrasive, and unlikely to cause erosion. Some antonyms for erosive are constructive, restorative, protective, and preservative. Examples of materials that could be described as such include protective coatings for metal, healing ointments for skin, and preservative treatments for wood. In many cases, a balance must be struck between protective and erosive qualities, as the most effective preservative treatments may be somewhat erosive in nature. Overall, antonyms for "most erosive" emphasize gentleness and protection over damage and abrasion.