Lewis & Short

mendax, dācis, adj. [mentior], given to lying, mendacious; subst., a liar.

  1. I. Lit.: mendacem esse adversus aliquem, Plaut. Poen. 1, 2, 188: cum mendaci homini, ne verum quidem dicenti, credere soleamus, Cic. Div. 2, 71, 146: Carthaginienses fraudulenti et mendaces, id. Agr. 2, 35, 95: aretalogus, Juv. 15, 16.
    As subst.: mendax, dācis, m., a liar.
    Prov.: mendacem memorem esse oportet, a liar should have a good memory, Quint. 4, 2, 91.
    Comp.: Parthis mendacior, Hor. Ep 2, 1, 112.
    Sup.: mendacissimus, the greatest liar, Plaut. Rud. 3, 4, 48.
    With gen.: si hujus rei me mendacem esse inveneris, Plaut. As. 5, 2, 4.
    With dat.: saepe fui mendax pro te mihi, Ov. H. 2, 11.
    With in and acc.: in parentem, Hor. C. 3, 11, 35; for which adversum, Plaut. Poen. 1, 2, 188.
    With in and abl.: in tenui farragine, Pers. 5, 77.
  2. II. Transf., of inanim, and abstr. things, lying, false, deceptive; feigned, fictitious, counterfeit, not real, etc. (mostly poet.): mendacia visa, Cic. Div. 2, 62, 127: speculum, Ov. Tr. 3, 7, 38: fundus, that does not yield the expected fruits, Hor. C. 3, 1, 30: damnum, Ov. A. A. 1, 431: infamia, Hor. Ep. 1, 16, 39: os, Tib. 3, 6, 35: pennae, Ov. M. 10, 159: quidquid Graecia mendax audet in historia, Juv. 10, 174.
    Hence, adv.: mendācĭter, falsely, mendaciously (post-class.): praedicare, Sol. 1, 87.
    Sup.: mendacissime dicere, Aug. Mor. Eccl. 1, 17.