toxic
TOK-sikadjMeaning poisonous; harmful to living things
Memory hook TOX = POISON: keep AWAY. The bottle under the sink has a big warning label and a skull on it; what is inside is toxic, so the cat backs away.
Some common garden flowers are toxic to cats.
In context The old paint in the house was toxic: it contained lead, which can make children seriously ill if they swallow even tiny chips.
Similar poisonous, harmful, noxious
Opposite harmless, nontoxic, safe
From Late Latin toxicus, from Greek toxikon, poison smeared on arrows (from toxon, a bow).