The most common and most likely answer to this crossword clue is the 11 letter word INFLAMMABLE
I've seen this crossword clue in The Daily Telegraph
I
N
F
L
A
M
M
A
B
L
E
Buddy explains!
The straight part
We know that "that may catch fire" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that may catch fire = inflammable.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 INFLAMMABLE mean?
INFLAMMABLE noun- Any inflammable substance.
- Capable of burning; easily set on fire.
- Easily excited; set off by the slightest excuse; easily enraged or inflamed.