notion

The noun notion suggests a fleeting, vague, or imperfect thought: a bare notion of how to proceed. Thought, which reflects its primary emphasis on the mental process, may denote any concept except the more weighty and elaborate ones: I welcomed his thoughts on the subject. A thought came to him.  Idea, although it may refer to thoughts of any degree of seriousness or triviality, is commonly used for mental concepts considered more important or elaborate: We pondered the idea of the fourth dimension. The idea of his arrival frightened me. Conception suggests a thought that seems complete, individual, recent, or somewhat intricate: The architect’s conception delighted them.