INSIDIOUS definition: 1. (of something unpleasant or dangerous) gradually and secretly causing harm: 2. (of something…. Learn more. The adjective ' insidious ' has its roots in Latin, originating from the word 'insidiosus,' which means 'cunning' or 'treacherous.' This Latin term is derived from 'insidiae,' which refers to 'ambushes' or 'traps.' The word 'insidiae' itself has connections to 'insidere,' meaning 'to sit in' or 'to lie in wait.' Therefore, ' insidious ' carries the etymological idea of something lying in wait or working secretly to deceive or harm. In its modern usage, ' insidious ' describes things that are ... INSIDIOUS meaning : causing harm in a way that is gradual or not easily noticed Understand the Insidious , definitions, grammar, examples of use and its curiosities.
