Two characters in Jeffery Farnol's "Amateur Gentleman" give these definitions of a gentleman:
"A gentleman is a fellow who goes to a university, but doesn't have to learn anything; who goes out into the world, but doesn't have to work at anything; and who has never been black-balled at any of the clubs."
"A gentleman is (I take it) one born with the God-like capacity to think and feel for others, irrespective of their rank or condition.... One who possesses an ideal so lofty, a mind so delicate, that it lifts him above all things ignoble and base, yet strengthens his hands to raise those who are fallen - no matter how low."