Probably a variant spelling of Dawn, the English word for daybreak.
Deawn is probably a variant spelling of Dawn, the English word for daybreak. That makes the name bright in both meaning and imagery, since dawn has long suggested beginnings, renewal, and the first light of morning.
The altered spelling does not change the underlying symbolism, but it does give the name a more personal, contemporary appearance. As a given name, Deawn feels gentle and open, with a nature-based simplicity that has helped many names like it endure. It has the quiet optimism of a word-name, yet the spelling gives it a slightly unexpected edge. That balance between familiar meaning and uncommon form is often what keeps rare variants interesting.