The most common and most likely answer to this crossword clue is the 9 letter word OVERTIRED
I've seen this crossword clue in Financial Times
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More clues leading to the result OVERTIRED
Buddy explains!

The straight part
We know that "excessively weary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case excessively weary = overtired.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 OVERTIRED mean?
OVERTIRED verb- To tire excessively.
- To become excessively tired.
- Overly tired