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 park’s lake, Lake Allaman, is currently experiencing a harmful algae bloom. — Zuri Primos july 26, Kansas City Star, 26 July 2026

However, other research highlights AI's propensity for hallucinations, harmful omissions, and poor performance in unstructured, real-world medical cases. — Jesse Pines, Forbes.com, 26 July 2026

Insecticides, for example, can be harmful to humans, pets, and the environment in general, while traps are usually passive. — New Atlas, 26 July 2026

The goal is to reduce brain inflammation, improve blood flow, lower harmful proteins and give the brain a steadier supply of fuel. — Samantha Agate, Miami Herald, 25 July 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