harmful

1 of 2

adjective

harm·​ful ˈhärm-fəl 

: of a kind likely to be damaging : injurious

harmful chemicals

harmfully

ˈhärm-fə-lē 

adverb

harmfulness noun

harmfulness

2 of 2

noun

harm·​ful·​ness

plural -es

: the quality or state of being harmful

Synonyms of harmful

Adjective

• detrimental
• damaging
• dangerous
• adverse
• bad

Examples of harmful in a Sentence

Adjective

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

Recent Examples on the Web

Adjective

During closing arguments, Randi McGinn, an attorney representing the state, argued that Facebook profited off harmful content. — Mikella Schuettler, Fortune, 26 Sep. 2026

David Arredondo pleaded guilty in July to child molesting and dissemination of matter harmful to minors. — Meredith Colias-Pete, Chicago Tribune, 25 Sep. 2026

OurTime combines member reporting with systems that review potentially harmful interactions. — Miami Herald, 25 Sep. 2026

Scientists already know that this exposes them to harmful cosmic radiation, but how the absence of the field itself, separate from radiation, might affect human physiology is not very well understood. — Sharmila Kuthunur, Space.com, 25 Sep. 2026

Word History

First Known Use

Adjective

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