The most common and most likely answer to this crossword clue is the 6 plus 3 letter word TINDER BOX
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "Kindle with this/Kindle with this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case kindle with this/kindle with this = tinder box.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.
Crossword Answer definitions
TINDER BOX noun- A small container containing flint, steel, and tinder (dry, finely-divided fibrous matter), once used to help kindle a fire.
- (by extension) a place that is so dry and hot that there is danger of fire.
- (by extension) a potentially dangerous situation.