accretion

Peter Shafferの "Amadeus" を読んでいます。ト書きの個所からの引用です。

And out of the thundery roar writhes and rises the clear sound of a soprano, singing the Kyrie from the C Minor Mass. The accretion of noise around her voice falls away -- it is suddenly clear and bright -- then clearer and brighter.

"accretion of noise" とは何でしょうか？　辞書を見ます。
・Oxford English Dictionary: the process of new layers or matter being slowly added to something: the accretion of sand by wind action
・Cambridge English Dictionary: a gradual increase or growth by the addition of new layers or parts: The fund was increased by the accretion of new shareholders.
・Vocabulary.com: The process of increasing can be called accretion. Although you may say that stalactites "grow" from the ceilings of caves, they actually form from an accretion of limestone and other minerals.So what's the difference between an addition and an accretion? Addition implies adding to something that already exists, such as an addition to the cast (when a new actor joins an existing show). The noun accretion, on the other hand, implies an accumulation that causes increase, such as "an accretion of frost on the windows" or "an accretion of plaque on your teeth." The latter, of course, is why the dentist always begs you to floss and brush.

"accretion" は追加とは違うとの説明は英英辞書ならの解説ですね。