virtue – (n) an example of moral goodness or excellence.

courtesy (n) an act of civility or respect; an act of kindness or favor performed with politeness.

courteous – (adj) showing regard or thought for self and others in manners, speech, behavior, etc; marked by polished manners.

No one is too big to be courteous, but some are too little. – Anonymous

A tree is known by its fruit; a man by his deeds. A good deed is never lost; he who sows courtesy reaps friendship, and he who plants kindness gathers love.– St. Basil

Gratitude is the most exquisite form of courtesy. – Jacques Maritain