Source : Webster's Revised Unabridged Dictionary (1913)

Lettish \Let"tish\ (l[e^]t"t[i^]sh), a.
   Of or pertaining to the Letts. -- n. The language spoken by
   the Letts. See {Lettic}.

Source : WordNet®

Lettish
     n : the official language of Latvia; belongs to the Baltic
         branch of Indo-European [syn: {Latvian}]