Most important (7)
'most important' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for central that I've seen before include "Key" , "like this answer" , "Extremely important" , "Middle; crucial" , "Most important, principal" .)
'most important' is the definition.
('big' can be similar in meaning to 'important')
This is all the clue.
(Other definitions for biggest that I've seen before include "Extremely great" , "Superlatively large" , "Greatest in size" , "Largest" .)