Something that one has thought of or devised, especially when it is creative or clever. This harebrained scheme was your brother's brainchild, wasn't it?This feature is my brainchild, and I'm going to see it through till the end, don't worry.
brainchild
1. n. someone’s good idea viewed as an offspring of the brain. Is this your brainchild? It won’t work.
2. n. a person who has good ideas. The boss’s new brainchild seems to have gone dry.