De*crease" (?), v. i. [imp. & p. p. Decreased (?); p. pr. & vb. n. Decreasing.] [OE. decrecen, fr. OF. decreistre, F. décroître, or from the OF. noun (see Decrease, n.), fr. L. decrescere to grow less; de + crescere to grow. See Crescent, and cf. Increase.] To grow less, -- opposed to increase; to be diminished gradually, in size, degree, number, duration, etc., or in strength, quality, or excellence; as, they days decrease in length from June to December.

He must increase, but I must decrease.

Syn. -- To Decrease, Diminish. Things usually decrease or fall off by degrees, and from within, or through some cause which is imperceptible; as, the flood decreases; the cold decreases; their affection has decreased. Things commonly diminish by an influence from without, or one which is apparent; as, the army was diminished by disease; his property is diminishing through extravagance; their affection has diminished since their separation their separation. The turn of thought, however, is often such that these words may be interchanged.

The olive leaf, which certainly them told
The flood decreased.

Crete's ample fields diminish to our eye;
Before the Boreal blasts the vessels fly.

De*crease", v. t. To cause to grow less; to diminish gradually; as, extravagance decreases one's means.

That might decrease their present store.

De*crease", n. [OE. decrees, OF. decreis, fr. decreistre. See Decrease, v.] 1. A becoming less; gradual diminution; decay; as, a decrease of revenue or of strength.

2. The wane of the moon. Bacon.

• Of a quantity, to become smaller.
  
• To make (a quantity) smaller.
  
• An amount by which a quantity is decreased.