Meaning of the names of months and days

Exodus 23:13 - (...) make no mention of the name of other gods, neither let it be heard out of thy mouth.

January- (in Latin, Ianuarius) is named after Janus, the god of the doorway.

February- The Roman month Februarius was named after the Latin term februum, which means purification, via the purification ritual Februa.

Februa-  Roman festival of ritual purification, later incorporated into Lupercalia.

Lupercalia- pastoral festival to avert evil spirits and purify the city.

Lupercus- is the god of shepherds.

March- named for Mars, the Roman god of war who was also regarded as a guardian of agriculture and an ancestor of the Roman people through his sons Romulus and Remus

April- The Romans gave this month the Latin name Aprilis but the derivation of this name is uncertain. Possibly: Aphrilis for Aphrodite (Greek equivalent to Venus)

May- The month May was named for the Greek goddess Maia, goddess of fertility

June- named after the Roman goddess Juno, the goddess of marriage and the wife of the supreme deity Jupiter

July- in honor of the Roman general, Julius Caesar

August- in honor of Augustus, founder of the Roman Empire and its first Emperor

September- from Latin septem, "seven"

October- from the Latin "octo" meaning "eight"

November- from the Latin novem meaning "nine"

December- from the Latin word decem which means "tenth"

Sunday -- Sun's day

Old English sunnandæg "day of the sun"
Germanic sunnon-dagaz "day of the sun"
Latin dies solis "day of the sun"
Ancient Greek hemera heli(o)u, "day of the sun"

Monday -- Moon's day

Old English mon(an)dæg "day of the moon"
Latin dies lunae "day of the moon"
Ancient Greek hemera selenes "day of the moon"

Tuesday -- Tiu's day

Old English tiwesdæg "Tiw's (Tiu's) day" - English/Germanic god of war and the sky.
Latin dies Martis "day of Mars" - Roman god of war.
Ancient Greek hemera Areos "day of Ares" - Greek god of war.

Wednesday -- Woden's day

Old English wodnesdæg "Woden's day" - leader of the Wild Hunt, wod "violently insane" + -en "headship
Latin dies Mercurii "day of Mercury" -  Roman god of commerce, travel, theivery, eloquence and science.
Ancient Greek hemera Hermu "day of Hermes" - Greek god of commerce, invention, cunning, and theft.

  

Thursday -- Thor's day

Old Norse thorsdagr "Thor's day" - Norse god of thunder

Latin dies Jovis "day of Jupiter" - Jupiter (Jove) is the supreme Roman god
Ancient Greek hemera Dios "day of Zeus" - Greek god of the heavens

Friday -- Freya's day

 Germanic frije-dagaz "Freya's (or Frigg's) day" - Freya (Fria) is the Teutonic goddess of love, beauty, and fecundity
Latin dies Veneris "Venus's day" - Roman goddess of love and beauty
Ancient Greek hemera Aphrodites "day of Aphrodite" - Greek goddess of love and beauty 

Saturday -- Saturn's day

Old English sæter(nes)dæg "Saturn's day" - Roman and Italic god of agriculture
Latin dies Saturni "day of Saturn" - Roman and Italic god of agriculture
Ancient Greek hemera Khronu "day of Cronus" - the Greek god (Titan) who ruled the universe until dethroned by his son Zeus.