The period of time past midnight, but before you go to sleep. It's obviously past midnight, but you're goddamn sure its not tomorrow yet. It's something in-between. It's not yesterday, but it is morning. It's yestermorning.

Not to be used in the present. Before sleeping, you may only refer to the present as tomorrow's yestermorning.
by dominobes May 31, 2020
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Yesterday morning. Similar to 'yestereve' and 'yesternoon'
What time were you up yestermorn
by JimJams May 19, 2007
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