Notion
Etymology: [L. notio, fr. noscere to know: cf. F. notion. See Know.]
1. Mental apprehension of whatever may be known or imagined; an idea; a conception; more properly, a general or universal conception, as distinguishable or definable by marks or notæ. What hath been generally agreed on, I content myself to assume under the notion of principles. Sir I. Newton. Few agree in their notions about these words. Cheyne. That notion of hunger, cold, sound, color, thought, wish, or fear which is in the mind, is called the "idea" of hunger, cold, etc. I. Watts. Notion, again, signifies either the act of apprehending, signalizing, that is, the remarking or taking note of, the various notes, marks, or characters of an object which its qualities afford, or the result of that act. Sir W. Hamilton.
2. A sentiment; an opinion. The extravagant notion they entertain of themselves. Addison. A perverse will easily collects together a system of notions to justify itself in its obliquity. J. H. Newman.
3. Sense; mind. [Obs.] Shak.
4. An invention; an ingenious device; a knickknack; as, Yankee notions. [Colloq.]
1 more senses
5. Inclination; intention; disposition; as, I have a notion to do it. [Colloq.]
Shades of meaning
Fernald has no entry of its own for notion; he lists it under idea.
He lists it without comment; the entries above explain its neighbors.