The most common and most likely answer to this crossword clue is the 4 plus 2 plus 4 letter word KEEP IT DARK
K
E
E
P
I
T
D
A
R
K
More clues leading to the result KEEP IT DARK
Buddy explains!
The straight part
We know that "Don’t tell anyone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case don’t tell anyone = keep it dark.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.