Simple Definition of harmful

from our Learner's Dictionary

harmful

adjective

ˈhɑɚmfəl

: causing or capable of causing damage or harm

The chemical kills harmful [=dangerous] bacteria.

They claim that the drug has no harmful [=bad] side effects.

—often + to

These conditions can be harmful to plant/animal life.

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“Harmful.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/harmful. Accessed 18 Jun. 2026.

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