There are several antonyms for the word "filicic acid anhydride" such as basic, acidic, neutral, watery, hydrated, aqueous, and non-acidic. While filicic acid anhydride is an acid anhydride, basic refers to a substance with a pH greater than 7, which is the opposite of acidity. Neutral, on the other hand, is a term used for substances that have a pH of 7, which is neither acidic nor basic. Watery and hydrated refer to substances that are diluted with water and contain water molecules, respectively. Aqueous relates to solutions diluted with water, while non-acidic refers to substances that are not acidic.