Martinus is a Latin masculine name composed of Mars (Mars) and -inus (of the nature of).
Martin [William Searle 1897 Onomasticon Anglo-Saxonicum, page 349].
Martinus [Sir Henry Ellis 1833 A General Introduction to Domesday Book 2: 184].
Martinꝰ [Frank Thorn & Caroline Thorn 1979 Domesday Book 21 (Northamptonshire): chapter 18, paragraph 79].
Martīnus [Patrick Hanks & Flavia Hodges 1988 A Dictionary of Surnames, page 350].
“Mars, who, as father of Romulus, was the primogenitor of the Roman people, the god of war, of husbandry, of shepherds and seers” [Ethan Andrews 1850 A copious and critical Latin-English lexicon, page 927].
“-īnus, -īna, -īnum, added to the names of persons, animals, or material things, and to some other words, with the sense ‘of’ or ‘pertaining to’, ‘of the nature of’” [Sir James Murray 1901 A new English dictionary on historical principles, 1st edition, 5 (I, J, K): 237].
“the Latin name Martinus. This was probably originally derived from Mars (genitive Martis), the name of the Roman god of war (and earlier of fertility)” [Patrick Hanks & Flavia Hodges 1990 A Dictionary of First Names, page 227].
A man named Martinus held land in Northamptonshire during the reign of King Eadweard III (the Confessor): “Martinꝰ liᵬe tenuit” (“Martin held it freely”) [Frank Thorn & Caroline Thorn 1979 Domesday Book 21 (Northamptonshire): chapter 18, paragraph 79].