The earliest extant Cornish lexicographical sources are glosses on Latin texts dating from around the end of the 9th century ad. The earliest of these glosses, “ud rocashaas”, appears above the adjective perosa ‘loathing’ in De Consolatione Philosophiae by Boethius, in a passage in which Philosophy tells Boethius, “For I have swift feathers, which fly up to the height of heaven. When quick Thought clothes herself in them, with loathing she despises the lands below (Terras perosa despicit)” (Breeze 2007: 367). Cashaas is the third person preterite ‘hated’ and has the Middle Cornish reflex casas. Ro is the perfective verbal particle and has the Middle Cornish reflex re. Breeze (2007: 368) explains ud as a gloss for terras, ‘land’. A further nineteen Cornish glosses are to be found in Smaragdus's 9th century Commentary on Donatus (Loth 1907). Three more Cornish glosses are to be found, written on a Latin text of the Book of Tobit, in Oxoniensis Posterior which dates from the 10th century (Stokes 1879: 21). There are a small number of Cornish glosses in the Prophetia Merlini by Joannis Cornubiensis, thought to have been written between 1153 and 1154 (Curley 1982: 222–223).

The Vocabularium Cornicum is an 11th or possibly 12th century multilingual glossary compiled from a corpus of glossed Latin texts. Lhuyd (1707: 222) recognized several interpretamenta that were to be found in Cornish but not found in Welsh. Lhuyd concluded that the Vocabularium is a Latin-Cornish glossary. Mills (2013a), however, shows that this glossary is in fact multilingual and, whilst it includes many Cornish glosses, it also incorporates Old Welsh, Old Breton, Old Norman French and Old English glosses. As a template, the Vocabularium Cornicum uses the earlier onomasiological Latin-English Lexicon of Ælfric, Abbot of Eynsham (c. 955 – c. 1010). Following Ælfric, the first entries in the Vocabularium Cornicum are Deus omnipotens, duy chefuidoc ‘almighty God’, Celum, nef ‘heaven’, Angelus, ail ‘angel’, Archangelus, archail ‘archangel’. The vocabulary then continues through the stages of the creation, including star, sun, moon, world, earth, sea and mankind. Then follow the parts of the body, the ranks of the church, members of the family, crafts and their implements, animals and plants, and household goods.