Loud
Old English hlūd, of West Germanic origin; related to Dutch luid, German laut, from an Indo-European root meaning ‘hear’, shared by Greek kluein ‘hear’, klutos ‘famous’ and Latin cluere ‘be famous’.
wiktionary
From Middle English loude, loud, lud, from Old English hlūd(“loud, noisy, sounding, sonorous”), from Proto-West Germanic *hlūd, from Proto-Germanic *hlūdaz, *hlūþaz(“heard”), from Proto-Indo-European *ḱlewtos(“heard, famous”), from Proto-Indo-European *ḱlew-(“to hear”). More at listen.
From Middle English loude, from Old English hlūde(“loudly”), from Proto-Germanic *hlūda, *hlūdô(“loudly”), related to Etymology 1.
etymonline
loud (adj.)
Middle English, from Old English hlud "noisy; making or emitting noise" (of voices, musical instruments, etc.), from Proto-Germanic *hludaz "heard" (source also of Old Frisian and Old Saxon hlud, Middle Dutch luut, Dutch luid, Old High German hlut, German laut "loud"), from PIE *klutos- (source also of Sanskrit srutah, Greek klytos "heard of, celebrated," Latin inclutus "renowned, famous," Armenian lu "known," Irish cloth "noble, brave," Welsh clod "praise, fame"), suffixed form of root *kleu- "to hear."
Of places, "noisy," from 1590s. Application to colors, garments, etc. ("flashy, showy") is by 1849. Also used colloquially of notably strong or bad smells. Paired with clear (adj.) at least since c. 1650.
loud (adv.)
Old English hlude "loudly, noisily," from Proto-Germanic *khludai (source also of Dutch luid, German laut), from the source of loud (adj.).
