insidious

[ in-sid-ee-uhs ]
/ ɪnˈsɪd i əs /
SEE SYNONYMS FOR insidious ON THESAURUS.COM

adjective

intended to entrap or beguile: an insidious plan.
stealthily treacherous or deceitful: an insidious enemy.
operating or proceeding in an inconspicuous or seemingly harmless way but actually with grave effect: an insidious disease.

Origin of insidious

1535–45; < Latin insidiōsus deceitful, equivalent to insidi(ae) (plural) an ambush (derivative of insidēre to sit in or on) + -ōsus -ous; see sit1

SYNONYMS FOR insidious

1 corrupting.
2 artful, cunning, wily, subtle, crafty.
SEE SYNONYMS FOR insidious ON THESAURUS.COM

OTHER WORDS FROM insidious

WORDS THAT MAY BE CONFUSED WITH insidious

insidious invidious

Words nearby insidious

inside track, inside track, the, insider, insider dealing, insider trading, insidious, insight, insightful, insigne, insignia, insignificance

Words related to insidiously

quietly, clandestinely, surreptitiously, covertly, privately, personally, furtively, stealthily, shrewdly, cunningly, craftily, confidentially, hush-hush, intimately, obscurely, slyly, privily, unobserved, intelligently

Example sentences from the Web for insidiously

British Dictionary definitions for insidiously

insidious
/ (ɪnˈsɪdɪəs) /

adjective

stealthy, subtle, cunning, or treacherous
working in a subtle or apparently innocuous way, but nevertheless deadly an insidious illness

Derived forms of insidious

insidiously, adverb insidiousness, noun

Word Origin for insidious

C16: from Latin insidiōsus cunning, from insidiae an ambush, from insidēre to sit in; see insessorial

Medical definitions for insidiously

insidious
[ ĭn-sĭd′ē-əs ]

adj.

Being a disease that progresses with few or no symptoms to indicate its gravity.

Other words from insidious

in•sid′i•ous•ly adv.