dec·re·ment 
(dĕkrə-mənt)
(dĕkrə-mənt)n.
1. The act or process of decreasing or becoming gradually less.
2. The amount lost by gradual diminution or waste.
3. Mathematics The amount by which a variable is decreased; a negative increment.
[Latin dēcrēmentum, from dēcrēscere, dēcrē-, to decrease; see DECREASE.]
dec′re·mental (-mĕntl) adj.