/ ˌdiːkəmˈpreʃn; NAmE / noun [ U ]
1.
a reduction in air pressure; the act of reducing the pressure of the air :
a decompression chamber (= a piece of equipment that divers sit in so that they can return slowly to normal air pressure after being deep in the sea)
decompression sickness (= severe pain and difficulty in breathing experienced by divers who come back to the surface of deep water too quickly)
—see also bends
2.
( technical ) the act or process of allowing sth that has been compressed (= made smaller) to fill the space that it originally took up