The most common and most likely answer to this crossword clue is the 6 letter word POISON
I've seen this crossword clue in The Guardian
P
O
I
S
O
N
More clues leading to the result POISON
- River being shown? It’s not what you’d want to drink
- Quiet prayer, not right: a threat to life?
- Fancy an idea containing this, for example
- It makes me sick when one’s taken in by spoon-bending
- Spoil gutted fish in Paris
- I snoop around to discover a cause of death
- I snoop around to discover cause of death
- Preferred drink with Hawaiian dish: scotch or negroni, for starters
Buddy explains!

The straight part
We know that "Spoil" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spoil = poison.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 POISON mean?
POISON noun- A substance that is harmful or lethal to a living organism.
- Something that harms a person or thing.
- A drink; liquor.
- Any substance that inhibits catalytic activity.
- To use poison to kill or paralyse (somebody).
- To pollute; to cause to become poisonous.
- To cause to become much worse.
- To cause (someone) to hate or to have unfair negative opinions.
- To inhibit the catalytic activity of.
- To place false information into (a cache) as part of an exploit.