The most common and most likely answer to this crossword clue is the 9 letter word SCUTTLING
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The straight part
We know that "Fast-moving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fast-moving = scuttling.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 SCUTTLING mean?
SCUTTLING verb- To cut a hole or holes through the bottom, deck, or sides of (as of a ship), for any purpose.
- To deliberately sink one's ship or boat by any means, usually by order of the vessel's commander or owner.
- (by extension, in figurative use) Undermine or thwart oneself (sometimes intentionally), or denigrate or destroy one's position or property; compare scupper.
- To move hastily, to scurry.
- The motion of one who scuttles.
- The act by which a vessel is scuttled.