FlatMappable doesn't capture what a monad is. For instance, you can do async programming using monads. Doesn't relate to FlatMappable.

I think you don't see the need for a new name if you don't grasp the concept. It's like in mathematics, you have tons of algebraic structures, like monoid, groups, fields, rings. They all represent categories of things which share some properties. You don't want to name the category by a one of its representatives, that would defeat the purpose of introducing an abstraction.