Late 16th century (in an earlier sense). From post-classical Latin numerositat-, numerositas large number, multitude (early 3rd cent. in Tertullian), rhythmic order from classical Latin numerōsus + -tās.
Definition of numerosity in US English:
numerosity
nounˌnjuːməˈrɒsɪti
Numerousness.
Origin
Late 16th century (in an earlier sense). From post-classical Latin numerositat-, numerositas large number, multitude (early 3rd cent. in Tertullian), rhythmic order from classical Latin numerōsus + -tās.