Pernicious (adjective)

1. Having a harmful effect, especially in a gradual or subtle way.
2. Deadly or potentially lethal.

Origin:

Late middle english: via old french from latin perniciosus, from pernicies 'ruin, destruction', from per- 'thoroughly' + nex, nec- 'death'.

Examples:

1. Smoking is a pernicious habit that can lead to serious health problems.
2. The pernicious influence of drugs can destroy lives and families.
3. The pernicious disease spread quickly through the village.
4. The pernicious ideology led to the collapse of the society.
5. The pernicious habit of procrastination can have a detrimental effect on one's career.