The most common and most likely answer to this crossword clue is the 9 letter word DEVIATION
I've seen this crossword clue in The Guardian
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More clues leading to the result DEVIATION
Buddy explains!
The straight part
We know that "A change of course" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a change of course = deviation.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 DEVIATION mean?
DEVIATION noun- The act of deviating; wandering off the correct or true path or road
- A departure from the correct way of acting
- The state or result of having deviated; a transgression; an act of sin; an error; an offense.
- (contract law) The voluntary and unnecessary departure of a ship from, or delay in, the regular and usual course of the specific voyage insured, thus releasing the underwriters from their responsibility.
- (Absolute Deviation) The shortest distance between the center of the target and the point where a projectile hits or bursts.
- For interval variables and ratio variables, a measure of difference between the observed value and the mean.
- The signed difference between a value and its reference value.