From resounding + -ly.

• (RP, America) IPA: /ɹɪˈzaʊndɪŋli/

resoundingly

1. With a loud, resonant sound.

   The bells tolled resoundingly.

   • 1859, Charles Dickens, chapter 6, in A Tale of Two Cities, London: Chapman and Hall, […], →OCLC ↗:

     The corner has been mentioned as a wonderful corner for echoes; it had begun to echo so resoundingly to the tread of coming feet, that it seemed as though the very mention of that weary pacing to and fro had set it going.

   • 1909, H[erbert] G[eorge] Wells, chapter XIII, in Ann Veronica, London: T[homas] Fisher Unwin:

     Then suddenly he seized a new preparation bottle that stood upon his table and contained the better part of a week's work—a displayed dissection of a snail, beautifully done—and hurled it across the room, to smash resoundingly upon the cemented floor under the bookcase;

2. (by extension) Emphatically, so as to be celebrated.

   The children resoundingly defeated the bully.