The dictionary definition of "brainchild" typically refers to an idea, plan, or invention that is the result of creative work or intellectual effort by an individual or group. It emphasizes the notion of something conceptualized or created through thought.
For example, in Merriam-Webster, the definition is: "a product of one's creative effort" or "an idea or plan that someone has thought of."
If you'd like more specific definitions or examples from a particular dictionary, please let me know!