The Collaborative International Dictionary of English v.0.48:

deflate \de*flate"\, v. t. [Pref. de- down + L. flare, flatus to
   blow.]
   To reduce from an inflated condition; used literally and
   metaphorically; as, to deflate a tire; to deflate
   expectations.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

deflate
    v 1: collapse by releasing contained air or gas; "deflate a
         balloon"
    2: release contained air or gas from; "deflate the air mattress"
    3: reduce or lessen the size or importance of; "The bad review
       of his work deflated his self-confidence" [syn: deflate,
       puncture]
    4: produce deflation in; "The new measures deflated the economy"
       [ant: inflate]
    5: reduce or cut back the amount or availability of, creating a
       decline in value or prices; "deflate the currency" [ant:
       inflate]
    6: become deflated or flaccid, as by losing air; "The balloons
       deflated" [ant: blow up, inflate]

The Free On-line Dictionary of Computing (19 January 2023):

deflate
deflate compression
deflate/inflate compression
inflate

    A compression standard derived
   from LZ77; it is reportedly used in zip, gzip, PKZIP,
   and png, among others.

   Unlike LZW, deflate compression does not use patented
   compression algorithms.

   Used as a verb to mean to compress (not decompress!) a file
   which has been compressed using deflate compression.  The
   opposite, inflate, means to decompress data which has been
   deflated.

   Deflate is described in RFC 1951.

   (1997-06-21)