Dismissed sound of instrument as anomaly (7)
I believe the answer is:
outlier
'anomaly' is the definition.
(I have seen 'Statistical anomaly' mean 'outlier' so perhaps 'anomaly' could also mean 'outlier')
'dismissed sound of instrument' is the wordplay.
'dismissed' becomes 'out' (I've seen this before).
'sound of' shows a homophone (sound like).
'instrument' becomes 'lyre' (lyre is a kind of instrument).
'lyre' is a homophone of 'lier'.
'out'+'lier'='OUTLIER'
'as' acts as a link.
(Other definitions for outlier that I've seen before include "Suburbanite" , "One detached from main grouping" , "Remote member of a group" , "Extreme deviation from the mean - our tile (anag)" , "Anomalous data point" .)