adjective del·e·te·ri·ous \ˌde-lə-ˈtir-ē-əs\

: damaging or harmful

Full Definition of DELETERIOUS

:  harmful often in a subtle or unexpected way <deleterious effects> <deleterious to health>
del·e·te·ri·ous·ly adverb
del·e·te·ri·ous·ness noun


  1. The chemical is deleterious to the environment.
  2. The drug has no deleterious effects on patients.
  3. In developing countries, the imposition of boundaries around national parks and protected areas has been deleterious for both people and wildlife. —Kristin B. Gunther, Association of American Geographers, 2002


Greek dēlētērios, from dēleisthai to hurt
First Known Use: 1643

Synonym Discussion of DELETERIOUS

pernicious, baneful, noxious, deleterious, detrimental mean exceedingly harmful. pernicious implies irreparable harm done through evil or insidious corrupting or undermining <the claim that pornography has a pernicious effect on society>. baneful implies injury through poisoning or destroying <the baneful notion that discipline destroys creativity>. noxious applies to what is both offensive and injurious to the health of a body or mind <noxious chemical fumes>. deleterious applies to what has an often unsuspected harmful effect <a diet found to have deleterious effects>. detrimental implies obvious harmfulness to something specified <the detrimental effects of excessive drinking>.
Medical Dictionary


adjective del·e·te·ri·ous \ˌdel-ə-ˈtir-ē-əs\

Medical Definition of DELETERIOUS

:  harmful often in a subtle or an unexpected way <the deleterious effects of radiation and chemotherapy on the marrow—Christine Gorman> <deleterious genes>


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