A cave in is a sudden COLLAPSE of the roof or walls of a cave due to natural causes such as erosion, seismic activity, or an excessive amount of water. The crossword solutions for the term 'cave in' include 'DESCEND' (7 letters), 'DECLINE' (7 letters), 'SAG' (3 letters), 'GIVE' (4 letters), 'LETUP' (5 letters), 'LOWER' (5 letters), 'ACCEDE' (6 letters), 'BUCKLE' (6 letters), and 'foldup' (6 letters), as well as 'COLLAPSE' (8 letters). All of these words describe the process of a cave in, from the initial weakening of the structure to its eventual COLLAPSE.