Definition of "Idea" :

noun: an approximate calculation of quantity or degree or worth

"A rough idea how long it would take."

noun: the content of cognition; the main thing you are thinking about

"It was not a good idea."

noun: a personal view

"He has an idea that we don't like him."

noun: your intention; what you intend to do

"The idea of the game is to capture all the pieces."

noun: (music) melodic subject of a musical composition

"The accompanist picked up the idea and elaborated it."