diminution
     n 1: change toward something smaller or lower [syn: {decline}]
     2: the statement of a theme in notes of lesser duration
        (usually half the length of the original) [ant: {augmentation}]
     3: the act of decreasing or reducing something [syn: {decrease},
         {reduction}, {step-down}] [ant: {increase}]
Source: WordNet® 2.0