Wiktionary
do the handsome thing
vb. To act liberally.
Usage examples of "do the handsome thing".
For another it was likely that his more loquacious self, in spite of all the discipline he could impose upon it, would, in moments of distraction or near-sleep, certainly torment him with observations on his new poverty -his inability to oblige Diana, to endow a chair of osteology, to do the handsome thing on occasion, to maintain some of the annuities he had promised, to undertake remote voyages in the Surprise when peace should come at last.
Jim acknowledged that Hanaud, when he wished, could do the handsome thing with a very good grace.