Emily Dickinson Lexicon

I-DE'A, n. [L. idea; Fr. idée; Gr. ιδεα, from ειδω, to see, L. video.]

1. Literally, that which is seen; hence, form, image, model of any thing in the mind; that which is held or comprehended by the understanding or intellectual faculties. I have used the word idea, to express whatever is meant by phantasm, notion, species, or whatever it is which the mind can be employed about in thinking. Locke. Whatever the mind perceives in itself, or is the immediate object of perception, thought or understanding, that I call an idea. Locke. The attention of the understanding to the objects acting on it, by which it becomes sensible of the impressions they make, is called by logicians, perception; and the notices themselves as they exist in the mind, as the materials of thinking and knowledge, are distinguished by the name of ideas. Encyc. art. Logic. An idea is the reflex perception of objects, after the original perception or impression has been felt by the mind. Encyc. In popular language, idea signifies the same thing as conception, apprehension, notion. To have an idea of any thing is to conceive it. In philosophical use, it does not signify that act of the mind which we call thought or conception, but some object of thought. Reid. According to modern writers on mental philosophy, an idea is the object of thought, or the notice which the mind takes of its perceptions. Darwin uses idea for a notion of external things which our organs bring us acquainted with originally, and he defines it, a contraction, motion or configuration of the fibers which constitute the immediate organ of sense; synonymous with which he sometimes uses sensual motion, in contradistinction to muscular motion.
2. In popular use, idea signifies notion, conception, thought, opinion, and even purpose or intention. Burke.
3. Image in the mind. Her sweet idea wandered through his thoughts. Fairfax. [A bad use of the word.]
4. An opinion, a proposition. These decisions are incompatible with the idea, that the principles are derived from the civil law.