Definition of insidious adjective from the Oxford Advanced Learner's Dictionary



BrE BrE//ɪnˈsɪdiəs//
; NAmE NAmE//ɪnˈsɪdiəs//
(formal, disapproving)
jump to other results
spreading gradually or without being noticed, but causing serious harm the insidious effects of polluted water supplies Word Originmid 16th cent.: from Latin insidiosus ‘cunning’, from insidiae ‘an ambush or trick’, from insidere ‘lie in wait for’, from in- ‘on’ + sedere ‘sit’.
See the Oxford Advanced American Dictionary entry: insidious