Example : Venomous snakes.
A virulent insect bite.

Synonyms : deadly, venomous

Example : An acerbic tone piercing otherwise flowery prose.
A barrage of acid comments.
Her acrid remarks make her many enemies.
Bitter words.
Blistering criticism.
Caustic jokes about political assassination, talk-show hosts and medical ethics.
A sulfurous denunciation.
A vitriolic critique.

Synonyms : acerb, acerbic, acid, acrid, bitter, blistering, caustic, sulfurous, sulphurous, vitriolic