The most common and most likely answer to this crossword clue is the 4 plus 2 letter word BELT UP
I've seen this crossword clue in The Sunday Telegraph
B
E
L
T
U
P
More clues leading to the result BELT UP
- For safety’s sake, a motorist should be quiet!
- To be safe in car, ... don’t chatter
- Quiet English officer in retro bar
- Live with large ram in silence
- “Clunk, Click – and do stop talking!”
- Put your safety strap on and be quiet
- Move very quickly to a higher position but be quiet
- Strap yourself in and shut it!
- Remark addressed to a back-seat driver that’s double-edged?
- Advice for 9, 10’s own safety
Buddy explains!
The straight part
We know that "Strap yourself in/shut it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case strap yourself in/shut it = belt up.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.