Many of the days of the week are named after ancient nature gods, many of which trace to PIE:
PIE sóh₂wl̥ (“sun”)
→ Proto-Germanic sunnǭ (“sun”)
→ Old English sunne (“sun”)
→ Old English Sunnandæg (“Sun's day”)
→ Middle English Sonday / Sunday
→ Sunday
PIE mḗh₁n̥s (“moon; month”)
→ Proto-Germanic mēnô (“moon”)
→ Old English mōna (“moon”)
→ Old English Mōnandæg (“Moon's day”)
→ Middle English Monenday / Monday
→ Monday
PIE deywós
→ Sanskrit deva, “god”
→ Latin deus, “god”
→ Old Norse Týr, the god
→ Old English Tīw
→ Tīwesdæg (“Tiw's day”)
→ Tuesday
PIE dyew- (“bright sky; daylight”)
→ deywós (“celestial one; god”)
→ Proto-Germanic Tīwaz
→ Old English Tīw
→ Tīwesdæg
→ Tuesday
The reconstruction exists for the remaining days too, but is more uncertain when tracing it to PIE:
PIE weh₂t- / related roots concerning excitement or inspiration
→ Proto-Germanic *Wōðanaz
→ Old English Wōden
→ Wōdnesdæg (“Woden's day”)
→ Wednesday
PIE (s)tenh₂- (“thunder”) (reconstruction/derivation has some uncertainty)
→ Proto-Germanic þunraz (“thunder”; the god Thunder/Thor)
→ Old English Þunor
→ Þunresdæg (“Þunor's day”)
→ Thursday
PIE prih₁- / preyH- (“to love; be dear”)
→ Proto-Germanic Frijjō (the goddess Frigg, approximately “beloved/dear one”)
→ Old English Frīg
→ Old English Frīgedæg (“Frīg's day”)
→ Middle English Fridai / Friday
→ Friday
Saturday is not known to trace to PIE:
Latin Saturnus
→ Old English Sætern(es)dæg (“Saturn's day”)
→ Saturday
Comments
And then there is Tuesday, for the forgotten god.
Many of the days of the week are named after ancient nature gods, many of which trace to PIE:
PIE sóh₂wl̥ (“sun”) → Proto-Germanic sunnǭ (“sun”) → Old English sunne (“sun”) → Old English Sunnandæg (“Sun's day”) → Middle English Sonday / Sunday → Sunday
PIE mḗh₁n̥s (“moon; month”) → Proto-Germanic mēnô (“moon”) → Old English mōna (“moon”) → Old English Mōnandæg (“Moon's day”) → Middle English Monenday / Monday → Monday
PIE deywós → Sanskrit deva, “god” → Latin deus, “god” → Old Norse Týr, the god → Old English Tīw → Tīwesdæg (“Tiw's day”) → Tuesday
PIE dyew- (“bright sky; daylight”) → deywós (“celestial one; god”) → Proto-Germanic Tīwaz → Old English Tīw → Tīwesdæg → Tuesday
The reconstruction exists for the remaining days too, but is more uncertain when tracing it to PIE:
PIE weh₂t- / related roots concerning excitement or inspiration → Proto-Germanic *Wōðanaz → Old English Wōden → Wōdnesdæg (“Woden's day”) → Wednesday
PIE (s)tenh₂- (“thunder”) (reconstruction/derivation has some uncertainty) → Proto-Germanic þunraz (“thunder”; the god Thunder/Thor) → Old English Þunor → Þunresdæg (“Þunor's day”) → Thursday
PIE prih₁- / preyH- (“to love; be dear”) → Proto-Germanic Frijjō (the goddess Frigg, approximately “beloved/dear one”) → Old English Frīg → Old English Frīgedæg (“Frīg's day”) → Middle English Fridai / Friday → Friday
Saturday is not known to trace to PIE:
Latin Saturnus → Old English Sætern(es)dæg (“Saturn's day”) → Saturday