Crystal/ˈkrɪstl/ Definition 1 of 4Pro Tip 1/3Natural Forms Crystal refers to a naturally occurring form, not just any regular solid. Amethyst is a type of crystal found in nature. Pro Tip 2/3Geometry Specific Use 'crystal' to highlight the geometric precision and regularity in natural solids. Diamonds are valued for their crystal structure. Pro Tip 3/3Metaphorical Use Crystal can metaphorically describe clarity of ideas or feelings. Her intentions were crystal clear.