D defs.my
Entry 3 senses Webster, 1913

Afterthought

/ăf'-tẽrth-ätˌ/ · Aft·er·thought · IPA /ˈæft.ɚ.θɔt/
01 n. Reflection after an act; later or subsequent thought.
  1. 1.
    Reflection after an act; later or subsequent thought.
  2. 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. 3.
    a feature or part added to a device, not thought of in its original design.