Definition of coalsey in English:

coalsey

(also coalsay, colesay)

Pronunciation /ˈkəʊlseɪ/

noun

dialect, rare British
  • The coalfish or saithe, Pollachius virens ; the young or fry of this.

Origin

Early 19th century; earliest use found in John Brockett (bap. 1788, d. 1842), antiquary. From coal + sey.