Afterthought

Aft·er·thought

Afterthought

n.
  1. Reflection after an act; later or subsequent thought.
  2. an action taken after another action and related to the first action, which would normally or optimally be done along with the first action; -- as, to do something as an afterthought.
  3. a feature or part added to a device, not thought of in its original design.