The most common and most likely answer to this crossword clue is the 10 letter word DILAPIDATE
I've seen this crossword clue in The Guardian
D
I
L
A
P
I
D
A
T
E
More clues leading to the result DILAPIDATE
Buddy explains!
The straight part
We know that "leave to decay" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leave to decay = dilapidate.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 DILAPIDATE mean?
DILAPIDATE verb- To fall into ruin or disuse.
- To cause to become ruined or put into disrepair.
- To squander or waste.