The most common and most likely answer to this crossword clue is the 9 letter word DAYSPRING
I've seen this crossword clue in The Times
D
A
Y
S
P
R
I
N
G
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The straight part
We know that "Dawn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dawn = dayspring.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 DAYSPRING mean?
DAYSPRING noun- The beginning of the day, or first appearance of light; the dawn; daybreak.