i·de·a 
(ī-dēə)
(ī-dēə)n.
1. Something, such as a thought or conception, that is the product of mental activity.
2. An opinion, conviction, or principle: has some strange political ideas.
3. A plan, purpose, or goal: She started school with the idea of becoming a doctor.
4. The gist or significance: The idea of the article is that investing in green technology can save you money in the long run.
5. A sense that something can happen; a notion or expectation: They have this idea that we can just drop what we're doing and go to the park.
6. Music A theme or motif.
7. Philosophy
a. In the philosophy of Plato, a non-physical form or archetype to which beings in phenomenal reality correspond only as imperfect replicas.
b. In the philosophy of Kant, a concept of reason that is transcendent but nonempirical.
c. In the philosophy of Hegel, absolute truth; the complete and ultimate product of reason.
8. Obsolete A mental image of something remembered.
[Middle English, from Latin, from Greek; see weid- in the Appendix of Indo-European roots.]
i·dea·less adj.
Synonyms: idea, thought, notion, concept, conception
These nouns refer to what is formed or represented in the mind as the product of mental activity. Idea has the widest range: “Human history is in essence a history of ideas” (H.G. Wells).
Thought is distinctively intellectual and stresses contemplation and reasoning: She gathered her thoughts before she spoke. Notion suggests an often intuitive idea or image conceived by the mind: “All that came to mind was a notion of galactic space, of spirals, the Horse Nebula, all of which were distant and mysterious and cold” (Craig Nova).
Concept and conception are applied to mental formulations on a broad scale: You seem to have absolutely no concept of time. “Every succeeding scientific discovery makes greater nonsense of old-time conceptions of sovereignty” (Anthony Eden).
These nouns refer to what is formed or represented in the mind as the product of mental activity. Idea has the widest range: “Human history is in essence a history of ideas” (H.G. Wells).
Thought is distinctively intellectual and stresses contemplation and reasoning: She gathered her thoughts before she spoke. Notion suggests an often intuitive idea or image conceived by the mind: “All that came to mind was a notion of galactic space, of spirals, the Horse Nebula, all of which were distant and mysterious and cold” (Craig Nova).
Concept and conception are applied to mental formulations on a broad scale: You seem to have absolutely no concept of time. “Every succeeding scientific discovery makes greater nonsense of old-time conceptions of sovereignty” (Anthony Eden).