means The quality or degree of being loud — how strong or intense a sound feels to the ear.

from From Old English 'hlud,' meaning loud, a word with deep Germanic roots and likely cousins in Dutch 'luid' and German 'laut.' These trace back to a Proto-Indo-European root '*kleu-,' meaning 'to hear' — so 'loud' originally meant something closer to 'heard,' i.e. the kind of sound that gets noticed. The '-ness' suffix, an old Germanic tool for turning adjectives into nouns, simply bundles the whole noisy quality into a single word.