Attack very light, just opening (6)

I believe the answer is:

assail

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'attack' is the definition.
('assail' can be a synonym of 'attack')

'very light just opening' is the wordplay.
'very' becomes 'assai' (I've seen this before).
'light just opening' becomes 'l' (I am not sure about this - if you are sure you should believe this answer much more).
'assai'+'l'='ASSAIL'

Can you help me to learn more?

(Other definitions for assail that I've seen before include "Trouble" , "Make violent attack on" , "Criticize" , "Attack, lash out" , "Slate" .)

I've seen this clue in The Telegraph.

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