Answer:

poison

Answer	Crossword Clue
POISON	Contaminate
POISON	Lethal stuff
POISON	Warning label word

POISON	Word seen on a skull and crossbones
POISON	Corrupt
POISON	Taint
POISON	Whodunit weapon
POISON	Hemlock, for one
POISON	Skull-and-crossbones stuff
POISON	What Mr. Yuk labels
POISON	Toxicology topic

POISON	Something harmful
POISON	Toxic substance
POISON	Toxin.
POISON	... hemlock.
POISON	Hemlock, for example.
POISON	Venom.
POISON	Kind of pen
POISON	Borgia potion

POISON	Another man's meat
POISON	Arsenic, e.g.
POISON	Pesticide
POISON	Arrow application
POISON	Exterminator's option
POISON	Negative influence
POISON	Murder method in Christie's "A Pocket Full of Rye"
POISON	Staple of Agatha Christie mysteries

POISON	Cause of Romeo's death
POISON	Toxic stuff
POISON	Venom
POISON	Strychnine
POISON	Scull-and-crossbones stuff
POISON	Toxicant
POISON	Arsenic e.g.
POISON	Strychnine e.g.

POISON	Feature of many a whodunit
POISON	Whodunit staple
POISON	Downfall in many an Agatha Christie novel
POISON	One of the nine weapons in 2008's expanded version of Clue