pernicious vs insidious

pernicious and insidious both are adjectives.

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

As adjectives, pernicious and insidious are synonyms defined as:

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

Other synonyms of pernicious include subtle.

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