The adjective "pernicious" comes from the Latin word pernicies, meaning "ruin" or ""destruction", which is formed from the prefix per- (meaning "completely") and the root nec- (related to "death" or "murder").   It entered Old French as pernicios, from the Latin word perniciosus meaning "destructive", which is formed from the prefix per- (meaning "completely") and nex, meaning "slaughter" or "death".   It entered English, around the early 15th century, meaning "evil" or "wicked," and was later used to describe things or conditions that are highly injurious or destructive, often in a gradual or subtle way. 

According to the Oxford English Dictionary (OED), the word "pernicious" was first used in English during the Middle English period,  with the earliest evidence dating to before 1425, in the medical text Guy de Chauliac's Grande Chirurgie. 

Examples of "pernicious" used in a sentence:  
"Yet this fear of the pernicious effects of property rights did not last for long." 
"The cuts in government funding have had a pernicious effect on local health services." 
"Yet some faculty perceive the pernicious effects of these forms and want to end them." 
"She thinks television has a pernicious influence on our children." 
"Some of those forms are even more pernicious than the old forms."
"And on the raging ocean main, Amid the stormy waves of death, And in the desert hurricane, And in the Plague's pernicious breath."

Just the facts:

PERNICIOUS Definition & Meaning - Merriam-Webster

PERNICIOUS Synonyms: 90 Similar and Opposite Words | Merriam-Webster Thesaurus