Synonyms for Decrease:

n.

crater, dip. increase, halve, top-slice, rebate, let up, cut back, trim down, shrivel. cutback, collapse, plunge. contraction (noun)
deflation, elision.
decrease (noun)
deduction, decrement, concentration, deflation, diminution, minify, lessen, abbreviation, reduction, abridgement, step down, Diminishment, shrinkage, truncation, contraction, compaction, erosion, curtailment, compression, fall, lessening, drop off, diminish, depletion.
depression (noun)
debasement, sinking, attenuation, depression, diminution.
diminishing, lessening (noun)
cutback, diminution, abatement, depression, shrinkage, reduction, discount, compression, contraction, loss.
event (noun)
lessening.
loss (noun)
dissolution, expropriation, ruin, debit, penalty, dissipation, forfeiture, setback, deprivation, privation, loss, attrition, dispossession, divestiture, exhaustion.
process (noun)
decrement.
shrinkage (noun)
abatement.
subtraction (noun)
depreciation, deletion, lessening, elision, subtraction, lowering.

v.

change (verb)
fall, diminish, lessen.
curtail (verb)
fragment, discontinue, reduce, minimize.
decrease (verb)
decrement, curtail, compress, deduct, die down, lessen, dwindle, abate, lower, abbreviate, truncate, shrink, recede, shorten, concentrate, abridge, diminish, contract, compact, drain, erode, subside, deplete, deflate.
depress (verb)
debase, attenuate, sink, depress.
diminish (verb)
downgrade, pare, trim, clip, shear, cull, prune, weed, condense, taper, shave, bob, crop, lighten, nip.
grow less or make less (verb)
drop, reduce, shrivel, let up, die down, subside, lighten, diminish, depreciate, shrink, contract, dwindle, lower, curtail, drop off, sink, lessen, abate.
lessening (verb)
abatement.
lose (verb)
lose, dispossess, drop, forfeit, exhaust, dissolve, dissipate, misplace, divest.
subtract (verb)
depreciate, discount, subtract, cut, dock, elide, delete.

Other synonyms:

cutback, crater, shrivel, plunge, top-slice, trim down. collapse, dip. halve, rebate. contract
lose.
curtail
minify.
cut short
clip.
deteriorate
sink.
drop-off
drop off.
economize
cut back.
lessen
lessening.
lighten
lighten.
lower
lower.
recede
recede.
reduce
cut back.
step-down
step down.
Other relevant words:
dip, collapse, rebate, increase, top-slice, fall, shrivel, abatement, cutback, minify, cut back, plunge.

Usage examples for decrease

  1. Such effects, however, tend to decrease as the movement advances, and the education and enlightenment of the masses increase. – The Social Work of the Salvation Army by Edwin Gifford Lamb