State in a loud and resolute way (6)
I believe the answer is:
affirm
'state' is the definition.
(I know that affirm is a more specific form of the action declare)
'a loud and resolute way' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'and' says to put letters next to each other.
'resolute way' becomes 'firm' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'f'+'firm'='AFFIRM'
'in' is the link.
Can you help me to learn more?
(Other definitions for affirm that I've seen before include "Emphatically state" , "Declare one's commitment (to)" , "Assert, avow" , "Make a formal declaration (rather than an oath)" , "State as a fact, assert" .)