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]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "deflate":
   abridge, beat down, belie, blow sky-high, blow up, break, cave,
   cave in, cheapen, collapse, compress, curtail, cut, cut back,
   cut down, cut prices, damp, dampen, decline, decrease, deduct,
   depreciate, depress, devaluate, diminish, disarm, disconfirm,
   discredit, disgrace, disprove, dive, downgrade, embarrass, enchain,
   explode, expose, fall, fall in, fall in price, fold, fold up, gag,
   give way, hamstring, handcuff, hobble, hog-tie, humble, humiliate,
   implode, invalidate, jew down, knock out, lessen, let down, lower,
   manacle, mark down, mortify, muzzle, negate, negative, nose-dive,
   paralyze, pare, plummet, plunge, prostrate, prove the contrary,
   puncture, put out, put to shame, reduce, retrench, roll back, sag,
   scale down, shame, shave, shorten, show up, silence, simplify,
   slash, slump, step down, strangle, take from, throttle, trim,
   truss up, tune down, undercut



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

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)