decrease

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive & transitive verb To become or cause to become less or smaller, as in number, amount, or intensity.
• noun The act or process of decreasing.
• noun The amount by which something decreases.

from The Century Dictionary.

• To become less; lessen; be diminished gradually in extent, bulk, quantity, or amount, or in strength, influence, or excellence: as, the days decrease in length from June to December.
• To make less; lessen; make smaller in dimensions, amount, quality, excellence, etc.; reduce gradually or by small deductions.
• noun A becoming less; diminution; wane (as applied to the moon); decay: as, a rapid decrease of revenue or of strength.
• noun The amount by which something is lessened; extent of loss or decrement: as, a great decrease in production or of income.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To cause to grow less; to diminish gradually.
• noun A becoming less; gradual diminution; decay.
• noun The wane of the moon.
• intransitive verb To grow less, -- opposed to increase; to be diminished gradually, in size, degree, number, duration, etc., or in strength, quality, or excellence.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive Of a quantity, to become smaller.
• verb transitive To make (a quantity) smaller.
• noun An amount by which a quantity is decreased.
• noun knitting A reduction in the number of stitches, usually accomplished by suspending the stitch to be decreased from another existing stitch or by knitting it together with another stitch. See Decrease (knitting).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the act of decreasing or reducing something
• verb decrease in size, extent, or range
• verb make smaller
• noun the amount by which something decreases
• noun a change downward
• noun a process of becoming smaller or shorter