Blossom beginning to fall down (6)
I believe the answer is:
flower
'blossom' is the definition.
('flower' can be a synonym of 'blossom')
'beginning to fall down' is the wordplay.
'beginning to' suggests taking the first letters.
'down' becomes 'lower' ('lower' can be a synonym of 'down'**).
The first letter of 'fall' is 'f'.
'f'+'lower'='FLOWER'
(Other definitions for flower that I've seen before include "the best one can pick" , "prime of life" , "Plant cultivated for blossoms" , "Garden plant" , "bloomer" .)