Lewis & Short

lapsăna (lampsăna), ae, f. (also lapsănium, ii, n., Hier. ap. Reg. S. Pachom. 52), = λαψάνη and λαμψάνη, an edible plant, charlock, Sinapis arvensis, Linn.; Plin. 20, 9, 37, § 96; Varr. R. R. 3, 16, 25; Cels. 2, 25.
Prov.: lapsanā vivere, to live on a meagre diet, Plin. 19, 8, 41, § 144.