When?

sidereal year
the time for the earth to make one complete revolution around the sun, relative to the fixed stars
 
dead
a time when coldness (or some other quality associated with death) is intense
 
term
a limited period of time
 
time scale
an arrangement of events used as a measure of duration
 
holiday
a day on which work is suspended by law or custom
 
hard times
a time of difficulty
 
ephemera
something transitory; lasting a day
 
Lincoln's Birthday
the day on which President Abraham Lincoln is remembered
 
Shevat
the fifth month of the civil year: the eleventh month of the ecclesiastical year in the Jewish calendar (in January and February)
 
split run
a print run of a newspaper during which some articles or advertisements are changed to produce a different edition
 
phase of the moon
a time when the Moon presents a particular recurring appearance
 
quarter
a fourth part of a year; three months
 
Gregorian calendar month
a month in the Gregorian calendar
 
school day
any day on which school is in session
 
semester
half a year; a period of 6 months
 
1980s
the decade from 1980 to 1989
 
test period
a period of time during which someone or something is tested
 
vice-presidential term
the tenure of a vice president
 
mid-October
the middle part of October
 
Shrove Tuesday
the last day before Lent
 
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