Significant second Oscar just unveiled? (9)
I believe the answer is:
momentous
'significant' is the definition.
(similar in meaning)
'second oscar just unveiled?' is the wordplay.
'second' becomes 'moment' (synonyms).
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'unveiled?' means to look at the middle letters (the word's outer letters are taken off).
The centre of 'just' is 'us'.
'moment'+'o'+'us'='MOMENTOUS'
(Other definitions for momentous that I've seen before include "major" , "of great significance" .)