verb (used with object), i·de·at·ed, i·de·at·ing. to form an idea, thought, or image of. verb (used without object), i·de·at·ed, i·de·at·ing.to form ideas; think. nounideatum. verb (tr) to form or have an idea of; to imagine or conceive v.c.1600, from idea + -ate (2). Related: Ideated; ideating.