Noun
(palaeography) The earliest style of Cyrillic writing developed from Greek uncial in the late 9th century, predominant in the 11th–14th centuries.
The handsomely fashioned writing is of the type described as polu-ustav (semi-uncial), which is midway between the stately ustav and the cursive, . . . —A. Aronson, Rabindranath Through Western Eyes
(Eastern Orthodoxy) A church statute prescribing daily prayer, feast days, and fasts.
While most of the service books are employed only in the conduct of public devotion, the psalter and the ustav are widely read works that are found in every household. —David Scheffel, In the Shadow of Antichrist: The Old Believers of Alberta