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The d rune (ᛞ) is called Daeg "day" in the Anglo-Saxon rune poem. The corresponding letter of the Gothic alphabet ᛞ d is called dags. This rune is also part of the Elder Futhark, with a reconstructed Proto-Germanic name *dagaz.
Its "butterfly" shape is possibly derived from Lepontic san.
Rune poems 
The name is only recorded in the Anglo-Saxon rune poem, since the rune was lost in the Younger Futhark:
ᛞ Dæg byþ drihtnes sond, deore mannum,
mære metodes leoht, myrgþ and tohiht
eadgum and earmum, eallum brice.
Day, the glorious light of the Creator, is sent by the Lord;
it is beloved of men, a source of hope and happiness to rich and poor,
and of service to all.
On runic inscription Ög 43 in Ingelstad, one Dagaz rune is translated using the Old Norse word for "day" as the personal name Dagr.
See also