pernicious

Definitions:

Destructive; hurtful; tending to injure or destroy.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)
Highly injurious or hurtful; destructive.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Killing utterly: hurtful: destructive: highly injurious.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Highly injurious; tending to injure or destroy, as health or morals; deadly; destructive.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Destructive to life.
- Warner's pocket medical dictionary of today. By William R. Warner. Published 1898. (adjective) (adj.) (adjective)
Perniciousness.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
Perniciously.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)
Destructive; hurtful; noxious.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)

Usage examples:

By 1830 the whole community seemed to have wakened to a sense of their pernicious and unprofitable effect, and laws were passed prohibiting them.
- Customs and Fashions in Old New England by Alice Morse Earle
If these same plants are gathered and thrown in a pile, the animals, through a kind of pernicious curiosity, may eat them with disastrous results.
- Special Report on Diseases of Cattle by U.S. Department of Agriculture J.R. Mohler
Since therefore this dogma of Osiander is both false and pernicious to consciences, it must be shunned and damned."
- Historical Introductions to the Symbolical Books of the Evangelical Lutheran Church by Friedrich Bente