The most common and most likely answer to this crossword clue is the 10 letter word SPRINKLING
I've seen this crossword clue in The Daily Telegraph
S
P
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More clues leading to the result SPRINKLING
Buddy explains!

The straight part
We know that "dash" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dash = sprinkling.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 SPRINKLING mean?
SPRINKLING verb- To cause (a substance) to fall in fine drops (for a liquid substance) or small pieces (for a solid substance).
- To cover (an object) by sprinkling a substance on to it.
- To drip in fine drops, sometimes sporadically.
- To rain very lightly outside.
- To baptize by the application of a few drops, or a small quantity, of water; hence, to cleanse; to purify.
- The action of the verb to sprinkle.
- A small amount of (some liquid, powder or other fine substance) that is sprinkled on to something.
- A light shower of rain.