lettic

from The Century Dictionary.

• Of or pertaining to the Letts or their congeners; related to the Letts: as, the Lettic language; the Samoghitians are a Lettic people. Lettic race is a general term for the Letts, Lithuanians, and Borussians or Old Prussians.
• noun Same as Lettish.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of or pertaining to the Letts; Lettish.
• adjective Of or pertaining to a branch of the Slavic family, subdivided into Lettish, Lithuanian, and Old Prussian.