In-sīd′i-ous, a.
(77), a. [Lat. insidiosus, from insidiæ, an ambush; It. & Sp. insidioso, Fr. insidieux. See INSIDIATE.]
- Lying in wait; watching an opportunity to ensnare or entrap; deceitful; sly; treacherous; — said of persons.
- Intending or intended to entrap; as, insidious arts.
Insidious disease (Med.), 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; circumscriptive; treacherous; deceitful; deceptive.