The most common and most likely answer to this crossword clue is the 9 letter word FOOLPROOF
I've seen this crossword clue in The Guardian
F
O
O
L
P
R
O
O
F
More clues leading to the result FOOLPROOF
- Completely safe dessert, one originally consumed by academic
- Sure can — fellow returned piano to top of house
- Demonstration by Charlie’s incapable of going wrong
- Infallible dessert with soft top
- Infallible measure put shortly on record? It might get slated
- Take in coppers – cover is solid
- Take in galley to be sure
- Infallible Charlie's evidence
Buddy explains!
The straight part
We know that "Sure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sure = foolproof.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 FOOLPROOF mean?
FOOLPROOF verb- To make foolproof.
- For a device: protected, or designed to be proof against misuse or error.
- For an idea or plan: infallible, or bulletproof.