diminution

noun

1. change toward something smaller or lower

   noun.process

   Synonyms decline

   Source: WordNet 3.0

2. the statement of a theme in notes of lesser duration (usually half the length of the original)

   noun.communication

   Antonyms augmentation

   Source: WordNet 3.0

3. the act of decreasing or reducing something

   noun.act

   Synonyms decrease reduction step-down

   Antonyms increase step-up

   Source: WordNet 3.0

4. The act of diminishing, or of making or becoming less; state of being diminished; reduction in size, quantity, or degree; -- opposed to <i>augmentation</i> or <i>increase</i>.

   noun

   Source: webster1913