Synonyms: insidious, pernicious, subtle
Definition: working or spreading in a hidden and usually injurious way
Usage: glaucoma is an insidious disease; a subtle poison
Similar words: harmful
Definition: causing or capable of causing harm
Usage: too much sun is harmful to the skin; harmful effects of smoking
Synonyms: pernicious, pestilent, deadly, baneful
Definition: exceedingly harmful
Similar words: noxious
Definition: injurious to physical or mental health
Usage: noxious chemical wastes; noxious ideas