magnitudo

Magnitudo, magnitudinis is third declension feminine, the -tudo abstract of magnus, and it sits in the same family as latitudo, longitudo and altitudo. All are feminine and all insert -in- before the endings, so the accusative is magnitudinem.

It runs from the physical to the moral without changing shape. Magnitudo urbis is plain size; magnitudo animi is greatness of soul, the standard Latin rendering of the Greek megalopsychia and the ancestor of English magnanimity. Roman writers also use it for the seriousness of a danger or a crime, where English would say gravity rather than size. The astronomical sense of magnitude, a star's brightness, is a much later borrowing and would have meant nothing to Cicero.