IN' The crossword solution for the term COLLAPSE with 'IN' is CAVE. A CAVE is a natural underground space that can be formed by the erosion of rocks over time. Caves are often associated with COLLAPSE, as they can form when the roof of a CAVE collapses due to the weight of the rock above it. COLLAPSE can also refer to the sudden and complete failure of a structure or system, which can be caused by a variety of factors such as poor design, inadequate maintenance, or natural disasters.