Definify.com

Webster 1913 Edition

(lĕt′tĭk)

Adj.

(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.

–

Noun.

(a)

The language of the Letts; Lettish.

(b)

The language of the Lettic race, including Lettish, Lithuanian, and Old Prussian.

Lettic ‎(not comparable)

Of or pertaining to the Latvian people or the Latvian language.
Of or pertaining to the Baltic family of languages.
- 1922, Melvil Dewey, Decimal classification and relative index for libraries and personal use
  "491.8 Other Slavonic [...] .9 Lettic .91 Old Prussian .92 Lithuanian .93 Lettish (Livonian)"

Latvian — see Latvian