The most common and most likely answer to this crossword clue is the 9 letter word FREEWHEEL
I've seen this crossword clue in The Daily Telegraph
F
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More clues leading to the result FREEWHEEL
Buddy explains!
The straight part
We know that "coast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coast = freewheel.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 FREEWHEEL mean?
FREEWHEEL noun- A device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft.
- (of a gear) To continue spinning after disengagement.
- (of a cyclist) To ride a bicycle without pedalling, e.g. downhill.
- (of a motorist) To operate a motor vehicle which is coasting without power, e.g. downhill.
- (by extension) To operate free from constraints.