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 definition defines the answer.
'start falling down' is the wordplay.
'start' says to take the initial letters.
'down' becomes 'lower' (synonyms).
The first 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" .)