January: January is the first month of the Gregorian calendar. Its name comes from Janus, the Roman god associated with beginnings and doorways, traditionally shown with two faces looking toward the past and the future. The Roman Latin form was Ianuarius, the month dedicated to Janus; historical references note that January had replaced March as the first month of the Roman year by no later than 153 BCE. It remains the first month in modern Gregorian usage, with January 1 serving as the conventional beginning of the civil year.

February: February is the second month of the Gregorian calendar and normally has 28 days, or 29 in a leap year. Its name derives from Latin Februarius, through Old French and Middle English, from februa—the name of a Roman purification feast held in this month. In the early Roman calendar it was placed at the end of the year, then moved between January and March in the fifth century BCE. The authoritative sources connect the name to the rite or festival, not to a securely established deity, so a direct attribution to a particular god should not be stated as certain.

March: March is the third month of the Gregorian calendar and has 31 days. It is named for Mars, the Roman god of war; its Latin form was Martius, literally “of Mars.” Martius was the first month of the early Roman calendar before January and February were added, so the name survived even though the month’s position later changed. English March developed through Middle English and Old French from Latin Martius mensis, “month of Mars.”

April: April is the fourth month of the Gregorian calendar and has 30 days. Its Latin Roman name was Aprilis, but its exact etymology is uncertain. One long-standing explanation derives it from Latin aperire, “to open,” evoking spring buds and blossoms; another proposal connects it with Aphrodite, the Greek counterpart of Venus, to whom the Romans regarded the month as sacred. These origins are best presented as possibilities rather than as a settled certainty.

May: May is the fifth month of the Gregorian calendar and has 31 days; in the Northern Hemisphere it is commonly the final month of spring. Its name is generally understood as deriving from Latin Maius, probably referring to Maia, a deity associated with growth. Some references note an alternative possibility connecting Maius with Latin magnus, “great,” and with the name Maia. The etymology is therefore a historical explanation with some uncertainty rather than an absolute conclusion.

June: June is the sixth month of the Gregorian calendar and has 30 days. The modern English name developed from Junius, the Latin name of the month in the Roman Republican calendar. References describe Junius as probably named for Juno, the chief Roman goddess, especially associated with women, marriage, childbirth, and fertility; this attribution is therefore presented as probable. June remains a standard month in the Gregorian calendar as a practical division of the solar year.

July: July is the seventh month of the Gregorian calendar. It is named for the Roman statesman Julius Caesar, not for a deity. Its earlier Latin name was Quintilis, meaning “fifth month,” a positional name from the early Roman calendar, when March began the year. After Caesar’s assassination in 44 BCE, the month was renamed Julius in his honor, and the English form July developed from that Latin name. July has 31 days.

August: August is the eighth month of the Gregorian calendar and has 31 days. In the early Roman calendar it was called Sextilis, Latin for “sixth month,” because March began the year. It was renamed Augustus in 8 BCE in honor of Augustus Caesar, Rome’s first emperor, not a deity. The name comes from a Latin honorific meaning “venerable,” “majestic,” or “worthy of honor”; the related English adjective august preserves the broader sense of dignity or grandeur.

September: September is the ninth month of the Gregorian calendar and has 30 days. Its name comes from Latin September, from septem, “seven,” because it was the seventh month of the early Roman year, which began in March. January and February were added later, but the inherited numerical name remained even after September became the ninth month. Authoritative references do not connect the name to a particular deity, ruler, or historical event.

October: October is the tenth month of the Gregorian calendar. Its name derives from the Latin octo, meaning “eight,” because it was the eighth month when the Roman year began in March. After January and February were placed before March, the inherited name remained even though October became the tenth month. The name refers to an old numerical position rather than a deity, person, or commemorated event. October has 31 days.

November: November is the eleventh month of the Gregorian calendar and has 30 days. Its name comes from Latin novem, meaning “nine,” because it was the ninth month of the early Roman year beginning in March. January and February were added later, while the inherited name remained. The Latin form was November, also recorded as Novembris, and this Roman naming tradition passed into the Julian and then Gregorian calendars. The name does not refer to a deity, ruler, or commemorative occasion.

December: December is the twelfth month of the Gregorian calendar. Its name derives from Latin decem, meaning “ten,” because it was the tenth month in the early Roman calendar before January and February were added. The name therefore preserves an older Roman numbering system rather than describing a modern seasonal or religious meaning, and the sources do not attribute it to a particular god or historical event. The Roman name survived the Julian reform, and December has 31 days.