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

But environmental advocates say the emergency declaration wasn’t warranted and has been used to fast-track projects harmful to the environment. — Finnegan Belleau, Chicago Tribune, 1 Nov. 2026

Stay Out Of The Sunlight Leaving perfume bottles in the sun is harmful for reasons beyond heat alone. — Brandee Gruener, Southern Living, 1 Nov. 2026

Yogurt contains beneficial bacteria but might also grow harmful microbes, such as mold. — Amber J. Tresca, Verywell Health, 31 Oct. 2026

Pouring gasoline onto your lawn is both unsafe and environmentally harmful. — Timothy Dale, The Spruce, 31 Oct. 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