When?

novitiate
the period during which you are a novice (especially in a religious order)
 
eon
an immeasurably long period of time
 
outing
a day devoted to an outdoor social gathering
 
mid-December
the middle part of December
 
duty period
the time period during which you are at work
 
trimester
a period of three months; especially one of the three three-month periods into which human pregnancy is divided
 
fifties
the time of life between 50 and 60
 
chapter
any distinct period in history or in a person's life
 
lease
the period of time during which a contract conveying property to a person is in effect
 
bimillenary
the 2000th anniversary (or the celebration of it)
 
field day
a time of unusual pleasure and success
 
quarter
one of four periods into which the school year is divided
 
half-century
a period of 50 years
 
spring
the season of growth
 
uptime
a period of time when something (as a machine or factory) is functioning and available for use
 
Boxing Day
first weekday after Christmas
 
Pan American Day
a day celebrating political and economic unity among American countries
 
nap
a period of time spent sleeping
 
Reign of Terror
the historic period (1793-94) during the French Revolution when thousands were executed
 
Pascha
the Jewish feast of the Passover
 
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