adjective

pernicious

per-NISH-us/pərˈnɪʃəs/

Causing serious harm, especially gradually or subtly.

The termites have a pernicious effect inside the apparently sound beam.

A substantial wooden support beam appears sound outside, but a cutaway reveals termites quietly consuming its interior, leaving extensive tunnels and a dangerously thin shell.

Etymology

perLatincompletely

+nicLatinviolent death, murder

+iousLatinfull of, characterized by

“Completely” and “violent death” combine behind the Latin sense “destruction, death, ruin.” That destructive force survives in the selected meaning, even when the harm works gradually or subtly.

In context

The Scottish Parliament105:18

hate crime is pernicious and deeply damaging.

Scottish Conservative and Unionist Party Debate: Repealing the Hate Crime Act - 17 April 2024

More examples

She challenged the pernicious assumption.
The policy produced subtle but pernicious consequences.
The report exposed a pernicious pattern of exploitation.

Forms

pernicious · more pernicious · most pernicious

perniciously adverb — in a seriously harmful way

Similar words

harmful: Harmful is general; pernicious emphasizes serious, often subtle or gradual harm.
insidious: Insidious emphasizes concealed or gradual development; pernicious emphasizes the damaging effect.