From Latin: uncus (“curve”). Uncial is a calligraphy script with rounded, unjoined letters. It was used in Latin and Greek manuscripts of the fourth to ninth centuries CE. The letters are similar to modern English capitals, but more rounded, seen especially in the E, M and U (rather than V). Modern English capital letters are derived from uncial letter forms. Web resource here.
Gallican Psalter with Canticles and Litanies. From Corbie Abbey, France. Second half of the 9th c. Zentralbibliothek Zürich, Ms. Car. C 161, folio 1 recto.