The most common and most likely answer to this crossword clue is the 11 letter word COORDINATED
I've seen this crossword clue in The Times
C
O
O
R
D
I
N
A
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D
Buddy explains!

The straight part
We know that "harmonised" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case harmonised = coordinated.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.
Crossword Answer definitions
COORDINATED verb- To synchronize (activities).
- To match (objects, especially clothes).
- Organized, working together, cooperating
- Physically graceful or skillful
- Having coordinate bonds