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

Fires that burn at low temperature produce more harmful gases than hot fires. — Eric Niiler, Los Angeles Times, 6 July 2026

Think of it as skincare in disguise, locking in at least 12 hours of moisture while shielding you from harmful UV rays. — Tanya Sharma, InStyle, 4 July 2026

Meta said the changes were designed to reduce exposure to potentially harmful content and create safer online experiences for younger users. — Larry Magid, Mercury News, 2 July 2026

The agency is also monitoring for cyanobacteria, formerly known as blue-green algae, which can form harmful algal blooms that pose risks to people and animals. — Madison Smalstig july 3, Sacbee.com, 3 July 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