pernicious
- Having a harmful effect in a gradual or subtle way that is difficult to detect; deadly or destructive.
In a sentence
- The report warned of the pernicious influence of misinformation spreading unchecked on social media.
- Pernicious anemia results from a chronic inability to absorb sufficient vitamin B12.
Usage note. Pernicious emphasizes slow, subtle, or insidious harm rather than sudden damage; it is a stronger and more formal word than simply 'harmful.'
Where it comes from
English pernicious · entered English early 16th c.
From Latin 'perniciosus,' meaning 'destructive, ruinous,' derived from 'pernicies,' meaning 'ruin, destruction,' formed from 'per-' (thoroughly) and 'nex' (genitive 'necis'), meaning 'violent death.' It entered English in the early 16th century.