alleviation,
easement,
easing,
relief (law) the privilege of using something that is not your own (as using another's land as a right of way to your own land)
decompression -
restoring compressed information to its normal form for use or display
decipherment,
decoding,
decryption the activity of making clear or converting from code into plain text; "a secret key or password is required for decryption"
