Carbonic acid; if two, the one containing the less amount of oxygen takes the termination -ous and the other the termination -ic, e.g.
An acid terminating in -ous forms a salt ending in -ite, and an oxyacid ending in -ic forms a salt ending in -ate.
The affixes -ous and sub- refer to the compounds containing more of the positive element, -ic and per- to those containing less.