pernicious.

Harmful in a serious way, especially when the harm spreads gradually or is not immediately obvious.

Use it for

Words that belong together

• a pernicious influence
• pernicious effects

On the page

The settlement's most pernicious influence was the quiet belief that no one could leave.

Usage notes

Primary category: horror / gothic. Forms: Comparative more pernicious; superlative most pernicious when comparison is meaningful. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings. Established modern English lexical item. No separate regional spelling or grammatical inflection entry. Writing functions: evaluation, causation. Commonness: moderately common.