year Unit of time equal to 365,25 days. Synonym: Julian year microsecond millisecond nanosecond tropical year ten day A unit of time defining the number of days in multiples of 10. day decade A unit of count defining the number of decades (decade: quantity equal to 10 or time equal to 10 years). half hour hour minute [unit of time] month Unit of time equal to 1/12 of a year of 365,25 days. quarter hour running or operating hour A unit of time defining the number of hours of operation. half year (6 months) A unit of time defining the number of half years (6 months). second [unit of time] tenth minute tenth hour two week week