Lettonian,a.andn.|lɛˈtəʊnɪən| [f.mod.L. Lettōn-, Letto Lett + -ian. Cf. Lapponian, and F. Letton= Lett.] = Lettish. 1880Libr.Univ.Knowl. (N.Y.) VIII. 835 The Lettonian differs from the other Lithuanian dialects in having an admixture of Finnish words.