What does diurnal mean?

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From our dictionary:

di•ur•nal

Pronunciation: (dI-ûr'nl), [key]
adj.
1. of or pertaining to a day or each day; daily.
2. of or belonging to the daytime (opposed to nocturnal).
3. Bot.showing a periodic alteration of condition with day and night, as certain flowers that open by day and close by night.
4. active by day, as certain birds and insects (opposed to nocturnal).

n.
1. Liturgy.a service book containing offices for the daily hours of prayer.
2. Archaic.a diary.
3. Archaic.a newspaper, esp. a daily one.