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.).