KashubianPronunciation: /kəˈʃuːbɪən/Definition of Kashubian noun 1a native or inhabitant of Kashubia, a region of Poland west and north-west of Gdansk. 2 [mass noun] the Western Slavic vernacular language spoken by about 200,000 people in Kashubia. It is closely related to Polish. adjective relating to Kashubia, its people, or their language.