For the Notion (Idea):
* Whimsical: Suggests a fanciful or capricious idea, often lighthearted and imaginative.
* Outlandish: Signifies an idea that is bizarre, unusual, and often impractical.
* Preposterous: Implies an idea that is absurd, ridiculous, and completely unbelievable.
* Fanciful: Refers to an idea that is imaginative and unrealistic, often appealing to the emotions.
* Quixotic: Describes an idea that is idealistic, impractical, and based on unrealistic expectations.
For the Action:
* Impetuous: Refers to an action that is hasty, impulsive, and without careful thought.
* Reckless: Indicates an action that is careless and irresponsible, potentially leading to harm.
* Unpredictable: Describes an action that is difficult to foresee or anticipate.
* Eccentric: Suggests an action that is unusual, odd, and unconventional, but not necessarily negative.
* Capricious: Refers to an action that is unpredictable and based on whim or fancy.
Combining the Two:
* Flights of Fancy: This idiom perfectly captures the idea of both extravagant notions and erratic actions. It refers to imaginative, unrealistic ideas that lead to impulsive or unpredictable behavior.
* Unhinged: This term can describe both an outlandish notion and a wildly erratic action, implying a loss of control or sanity.
* Bizarre: This is a general term that can describe both an unusual idea and an unexpected action.
* Audacious: This term suggests both a bold, unconventional idea and a daring, risky action.
The best word for you will depend on the specific context. Consider the tone and intensity you want to convey.