The most common and most likely answer to this crossword clue is the 6 plus 4 letter word LITMUS TEST
I've seen this crossword clue in The Guardian
L
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T
M
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S
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T
More clues leading to the result LITMUS TEST
- What’s contained in chemical it must establish?
- Decisive assessment essential in disputed titles
- Elaborate titles about essential touchstone
- A sure indication drunk has to set out
- It has to — in case holding that is seen as an indication
- After having fired, has to set off indicator
- Get examination paper for this assessment?
- Key indicator in case covering appeal: a necessity
- Laboratory experiment, content of chemical it must establish
- Disputed titles will contain duty, providing definitive trial
Buddy explains!
The straight part
We know that "A sure indication" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a sure indication = litmus test.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.