The Collaborative International Dictionary of English v.0.48:

decompress \decompress\ v. i.
   to undergo the process of decompression.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

decompress \decompress\ v. t.
   to subject to the process of decompression.
   [PJC]

WordNet (r) 3.0 (2006):

decompress
    v 1: restore to its uncompressed form; "decompress data" [syn:
         decompress, uncompress] [ant: compact, compress,
         pack together]
    2: decrease the pressure of; "depressurize the cabin in the air
       plane" [syn: depressurize, depressurise, decompress]
       [ant: pressurise, pressurize]
    3: become less tense, rest, or take one's ease; "He relaxed in
       the hot tub"; "Let's all relax after a hard day's work" [syn:
       relax, loosen up, unbend, unwind, decompress, slow
       down] [ant: tense, tense up]

The Free On-line Dictionary of Computing (30 December 2018):

decompress

    To reverse the effects of data
   compression.

   (2001-01-30)