The most common and most likely answer to this crossword clue is the 9 letter word DECOMPOSE
D
E
C
O
M
P
O
S
E
More clues leading to the result DECOMPOSE
- Style of art millions submit is rot
- Green politician in party starts to spout environmental rot
- Poem’s code is nonsensical rot!
- Go off to erase notes?
- Break down artistic style with male model
- Break up with model after Medoc gets drunk
- Withdraw from office, committee being content to break up
- Ask to support alternative comedy, mostly rot
- Dopes come out as rotters do
- Hide half what Bach did? Rot!
Buddy explains!

The straight part
We know that "Decay" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case decay = decompose.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 DECOMPOSE mean?
DECOMPOSE verb- To separate or break down something into its components; to disintegrate or fragment
- To rot, decay or putrefy