Dagaz

The rune d (ᛞ) is called dæg ("day") in the Anglo-Saxon rune poem. The corresponding letter in the Gothic alphabet, 𐌳 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 the Lepontic san.

Rune Poems
The name is only preserved in the Anglo-Saxon rune poem, as the rune was lost in the Younger Futhark:

Rune Poem

Anglo-Saxon
ᛞ Dæg byþ drihtnes sond, deore mannum,
mære metodes leoht, myrgþ und tohiht
eadgum und earmum, eallum brice.

The day, the glorious light of the Creator, is sent by the Lord;
It is loved by men, a source of hope and happiness for the rich and the poor,
and a service for all.

Inscriptions
In the runic inscription Ög 43 in Ingelstad, a rune Dagaz is translated with the Old Norse word for "day" as the personal name Dagr.