Definitions
working or spreading in a hidden and usually injurious way
Word origin
From Middle French insidieux, from Latin īnsidiōsus (“cunning, artful, deceitful”), from īnsidiae (“a lying in wait, an ambush, artifice, stratagem”) + -ōsus, from īnsideō (“to sit in or on”), from in (“in, on”) + sedeō (“to sit”).
Used in a sentence
“Strong and vigorous man as he looks, Livingstone has been for years the victim of a secret and insidious disease.”
“At some point in time they may become the source of an insidious cancer.”
“The nurse always must be alert to signs of slow leak or insidious infiltration.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Subtly harmful”9 letters
Not quite right?
"Search similar patterns."
I________