Diminution
WordNet
noun
(1) The act of decreasing or reducing something
(2) The statement of a theme in notes of lesser duration (usually half the length of the original)
(3) Change toward something smaller or lower
WiktionaryText
Noun
- A lessening, decrease or reduction.
- The new emission standards have produced a measurable diminution in air pollution.
- The shortening of the notes of a melody or theme.