pernicious

per-NISH-us

meaning in plain English

Imagine a quiet weed spreading under the soil, slowly choking a garden. Something that is pernicious causes serious harm in a sneaky, hard‑to‑spot way.

Think a sneaky garden weed that spreads underground—pernicious, it silently kills the flowers.

for example

That was a very pernicious thing to happen.

A pernicious habit is like a tiny leak that eventually floods a house – it seems harmless at first, but over time it damages everything.