Noisy means making a lot of unwanted sound. A noisy room, noisy neighbours, too noisy.
The unwanted part is the whole of it: a concert is loud and a road is noisy, and the difference is whether anybody asked for the sound. Noisy neighbours are one of the commonest sources of complaint to councils. In data and engineering, noisy means full of random interference — a noisy signal, noisy data — which is a precise technical sense. Note noise, noisily; and a noisy minority.
1adjectivenoisyMaking a lot of unwanted sound.
“Our neighbours are so noisy that we can hear their music through the wall.”
2adjectivefullFull of random interference, of data or a signal.
“The signal from the old sensor is too noisy to give accurate readings.”
noisy is a quality of unwanted sound.
Latin
nausia
Old French
noise — a dispute, wrangle, strife, noise
Middle English
noyse
English
noise
English, today
noisy
Built from
From noise + -y. noise comes from Middle English noyse, noise, from Old French noise (“a dispute, wrangle, strife, noise”), of uncertain origin. According to some, from Latin nausia, nausea (“disgust, nausea”); according to others, from Latin noxia (“hurt, harm, damage, injury”); but neither explanation is satisfactory in regard to either form or sense. Potentially a reduced form of Old French enoiier (“to bother, to disturb”), from Latin inodio (“to make repulsive”) - which would make it a doublet of annoy (“to bother, to irritate”) and ennui (“boredom, jadedness, depression”). Compare pms nojé (“to bother, to annoy”), though this fails to explain the final /z/. Displaced native Old English swēġ.
Etymology from Wiktionary, CC BY-SA