Second-declension noun, singular only. <span class="searchmatch">Averruncus</span> in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette. “<span class="searchmatch">Averruncus</span>”, in William Smith, editor...
while the sigmatic aorist expresses a possible desire ("might want to"). <span class="searchmatch">Āverruncus</span> “averrunco”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary...