insidious vs pernicious

insidious and pernicious both are adjectives.

Word	Noun	Adjective	Verb	Adverb
insidious	No	Yes	No	No
pernicious	No	Yes	No	No

As adjectives, insidious and pernicious are synonyms defined as:

insidious and pernicious: working or spreading in a hidden and usually injurious way

Other synonyms of insidious include subtle.

insidious (adjective)	pernicious (adjective)
intended to entrap	working or spreading in a hidden and usually injurious way
working or spreading in a hidden and usually injurious way	exceedingly harmful
beguiling but harmful