Measure of noise intensity (7)
I believe the answer is:
decibel
'measure of noise intensity' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for decibel that I've seen before include "Noise unit" , "Unit relating to sound or power measurement" , "Measure of sound" , "Unit of measurement for loudness" , "Sound level unit" .)