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