The best is loud, but getting softer (6)
I believe the answer is:
flower
'the best' is the definition.
(flower can mean the best or elite)
'loud but getting softer' is the wordplay.
I cannot quite see how this works, but
'loud' could be 'f' (short for forte - 'loud' in music) and 'f' is found in the answer.
'softer' could be 'lower' ('low' can be similar in meaning to 'soft') and 'lower' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for flower that I've seen before include "One found in bed perhaps" , "Garden plant" , "River" , "Bloom" , "Plant cultivated for blossoms" .)