When?

market day
a fixed day for holding a public market
 
probation
a trial period during which an offender has time to redeem himself or herself
 
Holy Year
(Roman Catholic Church) a period of remission from sin (usually granted every 25 years)
 
quarter
a fourth part of a year; three months
 
half-life
the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
 
Solemnity of Mary
(Roman Catholic Church) a holy day of obligation
 
Ascension of the Lord
(Christianity) celebration of the Ascension of Christ into heaven; observed on the 40th day after Easter
 
night
a period of ignorance or backwardness or gloom
 
diamond wedding
the 60th wedding anniversary
 
latency stage
(psychoanalysis) the fourth period (from about age 5 or 6 until puberty) during which sexual interests are supposed to be sublimated into other activities
 
school year
the period of time each year when the school is open and people are studying
 
test period
a period of time during which someone or something is tested
 
Michaelmastide
the season of Michaelmas
 
Muharram
the first month of the Islamic calendar
 
drouth
a prolonged shortage
 
triple-crown season
a season of baseball during which a player wins the triple crown
 
hour
a special and memorable period
 
bloom
the best time of youth
 
epoch
a period marked by distinctive character or reckoned from a fixed point or event
 
pass
(military) a written leave of absence
 
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