Deep/diːp/ Definition 1 of 5Pro Tip 1/3Measure Depth Consider 'deep' for measurable depths like water, holes, or gaps. The cave was so deep, sunlight couldn't reach the bottom. Pro Tip 2/3Abstract Depth 'Deep' can describe the complexity or seriousness in abstract ideas. The book's themes are deep and require careful analysis. Pro Tip 3/3Emphasize Impact Use 'deep' to stress the strength or intensity of an effect. The movie's message struck a deep chord with many viewers.