noun

the quality of being magnanimous; a magnanimous act.

(This  word is a derivative of the word magnanimous which in turn means showing noble sensibility or high minded)

source: the free dictionary by Farlex

I stumble on to the word “magnanimity” while reading chapter one of the Quicksand. It was use in the context “the exemplification of the white man’s magnanimity” . I believe  the word was used to emphasize the idea of how highly the white man is portrayed in Naxos. (refer to chapter 1 of Quicksand by Nella Larsen).