Source : Webster's Revised Unabridged Dictionary (1913)

Notion \No"tion\, [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 not[ae].

            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.]

   5. Inclination; intention; disposition; as, I have a notion
      to do it. [Colloq.]

Source : WordNet®

notion
     n 1: a vague idea in which some confidence is placed; "his
          impression of her was favorable"; "what are your
          feelings about the crisis?"; "it strengthened my belief
          in his sincerity"; "I had a feeling that she was lying"
          [syn: {impression}, {feeling}, {belief}, {opinion}]
     2: a general inclusive concept
     3: an odd or fanciful or capricious idea; "the theatrical
        notion of disguise is associated with disaster in his
        stories"; "he had a whimsy about flying to the moon";
        "whimsy can be humorous to someone with time to enjoy it"
        [syn: {whim}, {whimsy}, {whimsey}]
     4: (usually plural) small personal articles or clothing or
        sewing items; "buttons and needles are notions"