Harmful
Harmful adjective - Causing or capable of causing harm.
Usage example: DDT has been proven to be extremely harmful to the environment
Lethal is a synonym for harmful in noxious topic. In some cases you can use "Lethal" instead an adjective "Harmful", when it comes to topics like pernicious.
Lethal
Lethal adjective - Likely to cause or capable of causing death.
Usage example: we were lucky that the snake's venom wasn't lethal, and our friend turned out to be all right
Harmful is a synonym for lethal in dangerous topic. You can use "Harmful" instead an adjective "Lethal", if it concerns topics such as pernicious, deadly.
Nearby Word: lethality
Mutual synonyms
Both words in one sentence
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Captain Planet and the Planeteers: Not quite lethal, but far more harmful than it appeared — Ma-Ti uses the power of heart to communicate with animals telepathically.
Source: Lethal Harmless Powers - Part of the ritual to become a Ranger involved drinking something that was not harmful to Minbari, but potentially lethal to humans.
Source: Loophole Abuse / Live-Action TV - The story may reveal the battery is being taken advantage of, if not outright enslaved, and the extraction of the Living Battery's energy is harmful, traumatizing, or even lethal.
Source: Living Battery
Cite this Source
Lethal and Harmful. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/harmful/lethal
Harmful & Lethal. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/harmful/lethal>.
Lethal or Harmful. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/harmful/lethal.
Google Ngram Viewer shows how "harmful" and "lethal" have occurred on timeline