https://wiki.c2.com/?HydrogenHydroxide

Hydrogen Hydroxide
Water.
Specifically, water reacting as a base. When reacting as an acid its systematic name is Hydroxic Acid.
Oddly enough, water can be considered a molecule (H2O), or an ion group (H+ and OH-). Once I got that through my skull, the whole acid/base mess got much clearer.