|dē+ noun
Etymology: probably from French décompression, from dé- de- (from Old French des- ) + compression
: the act or process of releasing from pressure or compression: as
a. : reduction of pressure:
(1) : the decrease of atmospheric pressure experienced by a workman in an air lock when he is returning to the outside air from a caisson under compression or by an aviator when he ascends to a great height
(2) : the decrease of water pressure experienced by a diver when he ascends rapidly
b. : an operation or technique employed to relieve pressure upon an organ (as in fractures of skull or spine) or within a hollow organ (as in intestinal obstruction)