Saturday.
This day is named after the Norse god Saturn.

Sunday:
Germanic, day of the sun.

Monday:
Germanic, day of the moon.

Tuesday:
Tiu or Tiw from Tyr the Norse god of war.

Wednesday:
from Odin or Woden the Norse god.

Thursday:
from the Norse god Thor.

Friday:
from Frigg the Norse goddess of love.

Source: American Heritage Dictionary.