<span class="searchmatch">existitisset</span> third-person singular pluperfect active subjunctive of existō...
pluperfect extitissem, existitissem extitissēs, existitissēs extitisset, <span class="searchmatch">existitisset</span> extitissēmus, existitissēmus extitissētis, existitissētis extitissent...