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.
A decrease in knitting is 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.
decrease in size, extent, or range; "The amount of homework decreased towards the end of the semester"; "The cabin pressure fell dramatically"; "her weight fall to under a hundred pounds"; "his voice fell to a whisper"