“tertium”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
“tertium”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
tertium in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
tertium in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.