What does Britannus mean in Latin?

Britannus, a noun, means “a Briton; a Breton”.

What is the genitive of Britannus?

The genitive singular is Britannī. Britannus is masculine, second declension.

In classical Latin, [brɪˈtan.nʊs]; in ecclesiastical (church) Latin, [briˈtan.nus].

noun · masculinesecond declension

Britannus m sg (genitive Britannī)

Classical[brɪˈtan.nʊs]Ecclesiastical[briˈtan.nus]

See Britannia.

adjectivefirst/second-declension adjective

Britannus²

Britannus (feminine Britanna, neuter Britannum)

Classical[brɪˈtan.nʊs]Ecclesiastical[briˈtan.nus]

singular
form	masculine	feminine	neuter
nominative	Britannus	Britanna	Britannum
genitive	Britannī	Britannae	Britannī
dative	Britannō	Britannae	Britannō
accusative	Britannum	Britannam	Britannum
ablative	Britannō	Britannā	Britannō
vocative	Britanne	Britanna	Britannum

plural
form	masculine	feminine	neuter
nominative	Britannī	Britannae	Britanna
genitive	Britannōrum	Britannārum	Britannōrum
dative	Britannīs	Britannīs	Britannīs
accusative	Britannōs	Britannās	Britanna
ablative	Britannīs	Britannīs	Britannīs
vocative	Britannī	Britannae	Britanna

Charlton Lewis's shorter dictionary for students: the same scholarship in plain, modern definitions.

Britannus adj.,

of Britain: causidici, Iu.: esseda, Pr.

See Britannia.