The most common and most likely answer to this crossword clue is the 10 letter word PREDICATED
I've seen this crossword clue in The Guardian
P
R
E
D
I
C
A
T
E
D
Buddy explains!

The straight part
We know that "Declared" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case declared = predicated.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 PREDICATED mean?
PREDICATED verb- To announce, assert, or proclaim publicly.
- To assume or suppose; to infer.
- (originally United States) to base (on); to assert on the grounds of.
- (grammar) To make a term (or expression) the predicate of a statement.
- To assert or state as an attribute or quality of something.