Abstract In the Lithuanian and Latvian languages, forms of adjective degrees do not have a common etymological basis. The New Curonian (Kuresnieku) language which is a relatively new Baltic geolect has preserved a fairly distinct archaic layer of phonetics and grammar, where one can look not only for the archaisms of the western dialects of the Latvian language but also for traces of the substrate of Old Curonian. Although synthetic forms of the degrees of adjectives with the suffix -āk- are used in the current Latvian language area they are almost unknown in New Curonian. The forms of the comparative degree are made with the particle juo and an adjective of the positive degree. Analytical forms with the pronoun visu and the pronominal form of an adjective express the superlative degree. In the western Latvian and Lithuanian dialects and the Livonian language in Latvia, the relics of the analytical forms of the comparative and superlative degree are recorded in written sources and rarely in modern spoken language. Since a large part of the western dialects of the Lithuanian and Latvian languages take up the former territory of the old tribe, it may be assumed that the analytical forms of adjective degrees are possibly a sign of the substrate of Old Curonian.