A very loud shout ringing out below (10)
I believe the answer is:
thunderous
'a very' is the definition.
I can't tell whether this defines the answer.
'loud shout ringing out below' is the wordplay.
'loud shout ringing' becomes 'thous' (I can't explain this - if you can you should believe this answer much more).
'out' means one lot of letters goes inside another.
'below' becomes 'under' ('under' can be a synonym of 'below').
'thous' placed around 'under' is 'THUNDEROUS'.
Can you help me to learn more?
(Other definitions for thunderous that I've seen before include "Loud and rumbling" , "Deafening" .)