The most common and most likely answer to this crossword clue is the 8 letter word FIREBOMB
F
I
R
E
B
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M
B
More clues leading to the result FIREBOMB
Buddy explains!
The straight part
We know that "incendiary device" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case incendiary device = firebomb.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 FIREBOMB mean?
FIREBOMB noun- A weapon that causes fire, an incendiary weapon.
- To attack with a firebomb.