The most common and most likely answer to this crossword clue is the 4 letter word PYRE
I've seen this crossword clue in The Guardian
P
Y
R
E
Buddy explains!
The straight part
We know that "heap of wood for burning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heap of wood for burning = pyre.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 PYRE mean?
PYRE noun- A funeral pile; a combustible heap on which corpses are burned.
- Any heap or pile of combustibles.