1. Something, such as a thought or conception, that potentially or actually exists in the mind as a product of mental activity.
2. An opinion, conviction, or principle: has some strange political ideas.
3. A plan, scheme, or method.
4. The gist of a specific situation; significance: The idea is to finish the project under budget.
5. A notion; a fancy.
6. Music A theme or motif.
a. In the philosophy of Plato, an archetype of which a corresponding being in phenomenal reality is an imperfect replica.
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.