Cave in Definition 1 of 3Pro Tip 1/3Physical Weakness Used when structures or materials fail due to a lack of strength or integrity. The old shed's walls might cave in with the next storm. Pro Tip 2/3External Pressure Occurs due to outside forces, like weather or additional weight. The heavy snowfall made the roof cave in. Pro Tip 3/3Suddenness Highlights the abrupt nature of the collapse, often without warning. During the quake, the ceiling caved in.