Causing or capable of causing harm; injurious.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "harmful" in a sentence
"Chinese authorities have in recent months stepped up their already strict control of the flow of information online, including efforts this year to discourage the spread of what they term "harmful information" and "rumors"—words increasingly used for opinions and information not approved by the Communist Party."
"Obama, opening the forum, took another shot a Republicans in Congress for what he called a harmful practice of putting party above country."
"Hani Qawasmi, who had been considered a moderate civil servant acceptable to both factions, resigned due to what he termed harmful behavior by both sides."