The story
- Proto-Indo-European*de
- Proto-Indo-European*déh₁
- Proto-Italic*dē
- Latindē
- Old Frenchde
- Proto-Indo-European*h₁ey-
- Old Frenchdes
- Middle Englishdys
- English todaydice
From Middle English dys, plural of dy. See the etymology of die (etymology 2) for further information. The voiceless /s/ was most likely retained because the word felt like a collective term rather than a plural form (compare pence), and the spelling dice is a result of the pronunciation.
Etymology from Wiktionary, CC BY-SA 4.0.