Water can react as an acid in one reaction and as a base in another. What word describes a substance like this?

1. In its reaction with ammonia, water donates a proton and behaves as an acid. 2. In its reaction with acetic acid, water accepts a proton and behaves as a base. 3. A substance that can react as either an acid or a base is described as amphoteric. 4. A polyprotic acid is one that has more than one proton to donate, which is a separate idea. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 13: Types of reactions_