Lewis & Short

sŭper-văcānĕus, a, um, adj. [vacuus], over and above what is necessary, needless, unnecessary, superfluous, supervacaneous (class.): vasa, supernumerary, extra, Cato, R. R. 12: opus, i. e. done at leisure hours, Cic. Sen. 16, 56: litterae, id. Att. 16, 2, 5: commemoratio officiorum, id. Fam. 3, 5, 1: oratio, Liv. 22, 39: defensio Pauli, id. 45, 37: iter, id. 21, 13: actio, Just. 11, 12 fin.: instituta (opp. necessaria), Suet. Rhet. 1: quicquid supervacaneum sit, aut usum non habeat, obstare, Cic. N. D. 1, 35, 99; cf.: omnia ita nata atque ita locata sunt, ut nihil eorum supervacaneum sit, id. ib. 2, 47, 121: descriptio omnium corporis partium, in quā nihil inane, nihil sine causā, nihil supervacaneum, id. ib. 1, 33, 92: de timore supervacaneum est disserere, Sall. C. 51, 19; 58, 11: quin alter consul pro supervacaneo atque inutili habeatur, Liv. 10, 24.
* Adv.: sŭper-văcānĕō, uselessly, superfluously. Front. Ep. ad Caes. 4, 3 med.