harmful

adjective

harm·​ful ˈhärm-fəl 

: of a kind likely to be damaging : injurious

harmful chemicals

harmfully

ˈhärm-fə-lē 

adverb

harmfulness noun

Synonyms of harmful

• detrimental
• damaging
• dangerous
• adverse
• bad

Examples of harmful in a Sentence

DDT has been proven to be extremely harmful to the environment.

Recent Examples on the Web

The Times’ 2024 revelations that legal weed products, which were heavily advertised by the state as safe, contained harmful pesticides had a profound impact, with cannabis users voicing concern and anger. — Paige St. John, Los Angeles Times, 8 Nov. 2026

That means reversing harmful policies, holding those responsible for abuses accountable and making life more affordable for families. — Jose M. Muñoz, Chicago Tribune, 8 Nov. 2026

Without proper circulation, harmful fungi have an optimal environment for invading your lawn. — David Beaulieu, The Spruce, 7 Nov. 2026

They’ve been handed yet another free pass to keep emitting harmful air pollution without the protections that safeguard our health. — Elizabeth Bechard, Time, 6 Nov. 2026

Word History

First Known Use

14th century, in the meaning defined above

Rhymes for harmful

• armful

Kids Definition

harmful

adjective

harm·​ful ˈhärm-fəl 

: causing damage : injurious

harmfully

-fə-lē 

adverb

harmfulness noun

Legal Definition

harmful

adjective

harm·​ful

: of a kind likely to cause harm

harmfully adverb

harmfulness noun