The most common and most likely answer to this crossword clue is the 6 letter word SNEAKS
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More clues leading to the result SNEAKS
Buddy explains!

The straight part
We know that "moves stealthily" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moves stealthily = sneaks.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 SNEAKS mean?
SNEAKS noun- One who sneaks; one who moves stealthily to acquire an item or information.
- A cheat; a con artist.
- An informer; a tell-tale.
- A ball bowled so as to roll along the ground; a daisy-cutter
- A sneaker; a tennis shoe.
- A play where the quarterback receives the snap and immediately dives forward.