From un- + deleterious. <span class="searchmatch">undeleterious</span> (comparative more <span class="searchmatch">undeleterious</span>, superlative most <span class="searchmatch">undeleterious</span>) Not deleterious....
A deleterious mutation deleteriously deleteriousness nondeleterious <span class="searchmatch">undeleterious</span> harmful ^ Douglas Harper (2001–2025) “deleterious”, in Online Etymology...