Found 2 items, similar to insidiously.
English → English (WordNet) Definition: insidiously insidiously adv : in a harmfully insidious manner; “these drugs act insidiously” [syn: perniciously]
English → English (gcide) Definition: Insidiously Insidious \In*sid"i*ous\, a. [L. insidiosus, fr. insidiae an ambush, fr. insidere to sit in; pref. in- + sedere to sit: cf. F. insidieux. See Sit.] [1913 Webster] 1. Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons; as, the insidious foe. “The insidious witch.” --Cowper. [1913 Webster] 2. Intended to entrap; characterized by treachery and deceit; as, insidious arts. [1913 Webster] The insidious whisper of the bad angel. --Hawthorne. [1913 Webster] 3. Acting or proceeding unobserved or in a seemingly harmless manner, but slowly or eventually doing great damage; as, an insidious disease; an insidious plot. [PJC] Insidious disease (Med.), a disease existing, without marked symptoms, but ready to become active upon some slight occasion; a disease not appearing to be as bad as it really is. Syn: Crafty; wily; artful; sly; designing; guileful; circumventive; treacherous; deceitful; deceptive. -- In*sid"i*ous*ly, adv. -- In*sid"i*ous*ness, n. [1913 Webster]