Constantinus is a Latin masculine name composed of constans (constant) and -inus (of the nature of).
Custantin [Joseph Stevenson 1841 Liber Vitæ Ecclesiæ Dunelmensis, page 2].
Constantin [Joseph Stevenson 1841 Liber Vitæ Ecclesiæ Dunelmensis, page 5].
Constantinus [John Kemble 1840 Codex Diplomaticus Aevi Saxonici 2: 200].
Constantīnus [Ethan Andrews 1850 A copious and critical Latin-English lexicon, page 150].
Cosstantin [John Earle 1865 Two of the Saxon Chronicles Parallel, 1st edition, page 111].
Costontinus [John Earle 1865 Two of the Saxon Chronicles Parallel, 1st edition, page 114].
Constantine [Michael Swanton 2000 The Anglo-Saxon Chronicles, 2nd edition, page 104].
constans = Standing firm, firm, unchangeable, constant, immovable, uniform, invariable [Ethan Andrews 1850 A copious and critical Latin-English lexicon, page 362].
“-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].
A ruler named Constantinus witnessed a charter issued by King Æthelstan II on 13 September 934 at Buckingham: “✠ Ego Constantinus subregulus consensi et subscripsi” [John Kemble 1840 Codex Diplomaticus Aevi Saxonici 2: 200]. He has been identified as “Constantine, king of the Scots” [Susan Kelly 2012 Anglo-Saxon Charters 15: 353].