Wordnet 3.0
NOUN (1)
1. 
 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; 
[syn: Julian calendar, Old Style calendar]
WordNet (r) 3.0 (2006):
Old Style calendar
    n 1: 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 [syn: Julian calendar, Old Style calendar]