the world > physical sensation > hearing and noise > degree, kind, or quality of sound > loudness > [adjective] > increase of loudness
1810 A. Wilson Foresters in III. 187 Groaning we start! and, at the loudening war, Ask our bewilder'd senses where we are.
1864 R. F. Burton I. 183 A loudening hum of voices heralded a rush of warriors into the Uhon-nukon, or cleared space, with its central tree.