The question mark, also known as the interrogation point, query, and eroteme, is a punctuation mark that indicates an interrogative sentence, clause, or phrase in written English and many other languages.
1.
intended to entrap or beguile:
an insidious plan.
2.
stealthily treacherous or deceitful:
an insidious enemy.
3.
operating or proceeding in an inconspicuous or seemingly harmlessway but actually with grave effect:
an insidious disease.