Legal Definitions - O.S.

O.S.

Abbreviation for "Old Style."

• The date on the tombstone read "April 3, 1750 O.S."
• The book was printed in 1890 O.S.

O.S. stands for "Old Style" and is used to indicate a date that was recorded using the Julian calendar, which was replaced by the Gregorian calendar in most countries in the 16th century. The examples show how O.S. is used to indicate a date that was recorded using the Julian calendar.