This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Working or spreading harmfully in a subtle or stealthy manner: insidious rumors; an insidious disease.

adj. Intended to entrap; treacherous: insidious misinformation.

adj. Beguiling but harmful; alluring: insidious pleasures.

adj. Producing harm in a stealthy, often gradual, manner.

adj. Intending to entrap; alluring but harmful.

adj. Treacherous.

adj. Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; -- said of persons.

adj. Intended to entrap; characterized by treachery and deceit.

adj. Acting or proceeding unobserved or in a seemingly harmless manner, but slowly or eventually doing great damage.

Lying in wait; hence, deceitful; sly; treacherous.

Designed or adapted to entrap; deceptive; insnaring: as, insidious arts.

adj. beguiling but harmful

adj. intended to entrap

adj. working or spreading in a hidden and usually injurious way

"I mean, you've got Darth Sidious (as in "insidious," I assume) and then the even-more-obviously named Darths Maul and Tyrannus."

seductive    dangerous    unsafe    harmful   

insidious disease   

insidiousness    insidiously   

treacherous    deceitful    guileful    sly    circumventive    designing    wily    crafty    deceptive    artful   

fastidious    hideous    invidious   

subtle    treacherous    pernicious    seductive    malignant    malicious    irresistible    deceitful    artful    persistent