The Collaborative International Dictionary of English v.0.48:

Lettic \Let"tic\ (l[e^]t"t[i^]k), a.
   (a) Of or pertaining to the Letts; Lettish.
   (b) Of or pertaining to a branch of the Slavic family,
       subdivided into Lettish, Lithuanian, and Old Prussian. --
       n.
   (a) The language of the Letts; Lettish.
   (b) The language of the Lettic race, including Lettish,
       Lithuanian, and Old Prussian.
       [1913 Webster]