Mundane sound by Tom, say (7)
I believe the answer is:
humdrum
'mundane' is the definition.
(I've seen this before)
'sound by tom say' is the wordplay.
'sound' becomes 'hum' (humming is a kind of sounding).
'by tom say' becomes 'drum' (I can't justify this - if you can you should give a lot more credence to this answer).
'hum'+'drum'='HUMDRUM'
Can you help me to learn more?
(Other definitions for humdrum that I've seen before include "Droning sounds" , "Everyday, tedious" , "Common place" , "Uneventful - routine" , "Routine and monotonous" .)