The most common and most likely answer to this crossword clue is the 4 plus 5 letter word WIDE AWAKE
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The straight part
We know that "one’s fully aware" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one’s fully aware = wide awake.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WIDE AWAKE mean?
WIDE AWAKE adjective- Completely or fully awake
- Alert, vigilant or watchful
- A bird, the sooty tern.
- A type of hat with a broad brim made of black or brown felt.