The most common and most likely answer to this crossword clue is the 2 plus 3 plus 4 plus 5 letter word AS THE CROW FLIES
I've seen this crossword clue in The Daily Telegraph
A
S
T
H
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C
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O
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F
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S
More clues leading to the result AS THE CROW FLIES
- Oddly, in her case, it flows in a straight line
- See flow chart is repositioned straight
- Straight line dividing facts he mixed with falsehoods
- Getting straight to the point in a murder, perhaps
- Welsh factories abandoned directly
- Welsh factories redeveloped directly
- Welsh factories rebuilt in a straight line
- Direct rocket’s nose to separate over the moon, according to rhyme?
- Chaotic cartwheels? If so, get straight
- Directly watches for corruption and attempts to deceive
Buddy explains!

The straight part
We know that "directly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case directly = as the crow flies.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.