Martius

• mārtius (alternative case form)

From Mārs +‎ -ius. As a noun, ellipsis of Mārtius mēnsis m (“month of March”).

• (Classical Latin) IPA^(key): /ˈmaːr.ti.us/, [ˈmäːrt̪iʊs̠]
• (modern Italianate Ecclesiastical) IPA^(key): /ˈmar.t͡si.us/, [ˈmärt̪͡s̪ius]

Mārtius (feminine Mārtia, neuter Mārtium); first/second-declension adjective

1. of or belonging to Mars, the god of war; sacred to Mars
2. (figuratively) warlike, martial
3. of or belonging to the planet Mars
4. of or pertaining to the month of March, of March, the first month of the traditional Roman year or third month of the Gregorian calendar

In Classical Latin, month names were regularly used as adjectives, generally modifying a case-form of mēnsis m sg (“month”) or of one of the nouns used in the Roman calendar to refer to specific days of the month from which other days were counted: Calendae f pl (“calends”), Nōnae f pl (“nones”), Īdūs f pl (“ides”). However, the masculine noun mēnsis could be omitted by ellipsis, so the masculine singular forms of month names eventually came to be used as proper nouns.^[1]

The accusative plural adjective forms Aprīlīs, Septembrīs, Octōbrīs, Novembrīs, Decembrīs^[2] are ambiguous in writing, being spelled identically to the genitive singular forms of the nouns; nevertheless, the use of ablative singular forms in -ī and comparison with the usage of other month names as adjectives supports the interpretation of -is as an accusative plural adjective ending in Classical Latin phrases such as "kalendas Septembris".^[3]

First/second-declension adjective.

• mārtiālis

Mārtius m (genitive Mārtiī or Mārtī); second declension

1. The month of March.

Second-declension noun.

¹Found in older Latin (until the Augustan Age).

Borrowings:

Unsorted borrowings:

•   Roman calendar on Wikipedia.Wikipedia

• “Martius”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• “Martius”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers