The substance that yields a Cation plus the Hydroxyl ion in water is a Base.
A Cation is a positively charged ion. A Hydroxyl ion is an ion with a negative charge and is made up on one oxygen atom and one hydrogen atom. Bases are substances that promote chemical reactions. Dissociation is a process in which ionic compounds split into smaller particles.
In this case, the base acts by dissociation to yield a Cation plus a Hydroxyl ion in water.