› [C] a suggestion or plan for doing something: idea about sth The CTO should have ideas about where the company needs to be heading in terms of technology.come up with/have an idea He came up with the idea of promoting the two products together. new/fresh/innovative ideas They had great ideas but lacked the business know-how to turn an idea into a successful product. › [S] the purpose of, or reason for, doing something: The whole idea of budgeting is to control costs.