Julian calendar

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The solar calendar introduced by Julius Caesar in Rome in 46 BC, having a year of 12 months and 365 days and a leap year of 366 days every fourth year. It was eventually replaced by the Gregorian calendar.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The calendar which was used in the western world before the present-day Gregorian calendar. The Julian calendar differed in having all multiple-of-4 years as leap years.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the solar calendar introduced in Rome in 46 b.c. by Julius Caesar and slightly modified by Augustus, establishing the 12-month year of 365 days with each 4th year having 366 days and the months having 31 or 30 days except for February