Lewis & Short

vānĭdĭcus, a, um, adj. [vanus-dico], vain-speaking; false-speaking; subst., a liar (ante- and post-class. and rare): cum probis potius quam cum improbis vivere vanidicis, Plaut. Trin. 2, 1, 37; Amm. 16, 7, 2.