Even the best can start falling down (6)
I believe the answer is:
flower
'even the best' is the definition.
I can't tell whether this defines the answer.
'start falling down' is the wordplay.
'start' suggests taking the first letters.
'down' becomes 'lower' (synonyms).
The initial letter of 'falling' is 'f'.
'f'+'lower'='FLOWER'
'can' is the link.
Can you help me to learn more?
(Other definitions for flower that I've seen before include "prime of life" , "the best one can pick" , "Blossom" , "One found in bed perhaps" , "Garden plant" .)