Bad / Dangerous
tremor - A slight shaking movement, such as one caused by an earthquake or instability; also a subtle or faint sign of emotion, such as fear or excitement in the voice or body.

Because he was nervous, his voice had a significant tremor during the presentation.
caustic - Sarcastic or severely critical, often in a hurtful or biting manner; or able to burn or corrode organic tissue, typically referring to chemicals or substances.

The caustic chemical spilled onto the floor and quickly started to eat away at the floor surface.