Is it ensure, insure, or assure?
Old English hlud "noisy, making noise, sonorous," from West Germanic *khluthaz "heard" (cf. Old Frisian and Old Saxon hlud, Middle Dutch luut, Dutch luid, Old High German hlut, German laut "loud"), from PIE past participle *klutos- (cf. Sanskrit srutah, Greek klytos "heard of, celebrated," Armenian lu "known," Welsh clod "praise"), from root *kleu- "to hear" (see listen).
Application to colors first recorded 1849. The adverb is from Old English hlude, from Proto-Germanic *khludai (cf. Dutch luid, German laut). Paired with clear since at least c.1650.
in acoustics, attribute of sound that determines the intensity of auditory sensation produced. The loudness of sound as perceived by human ears is roughly proportional to the logarithm of sound intensity: when the intensity is very small, the sound is not audible; when it is too great, it becomes painful and dangerous to the ear. The sound intensity that the ear can tolerate is approximately 1012 times greater than the amount that is just perceptible. This range varies from person to person and with the frequency of the sound