From <span class="searchmatch">existless</span> + -ness. <span class="searchmatch">existlessness</span> (uncountable) (rare, literary) nonexistence 1912, Thomas Hardy, The Voice: Or is it only the breeze, in its listlessness...
From exist + -less. <span class="searchmatch">existless</span> (not comparable) (rare, literary) nonexistent <span class="searchmatch">existlessness</span>...
also Thesaurus:exist coëxist coexist existability existable existible <span class="searchmatch">existless</span> inexist postexist preexist superexist there exist unexist existence existent...