* Thought: This is the most common and general noun for thinking. It refers to the act of thinking itself, as well as the ideas or concepts produced by thinking.
* Cogitation: This is a more formal and literary word for thinking, often used to describe deep or serious thought.
* Contemplation: This noun refers to the act of thinking about something carefully and seriously.
* Reflection: Similar to contemplation, this word implies a thoughtful consideration of a subject.
* Idea: While not directly related to the act of thinking, it refers to the product of thinking.
The best noun to use will depend on the context and the specific nuance you want to convey.