The words cynic, cynical and cynicism are all related to the Greek word for ‘dog’. Indeed, a number of the words beginning cyn- in the dictionary are to do with dogs, eg cynophobia, aversion to and fear of dogs, cynoclept, dog-stealer, and cynanthropy, a species of madness in which a man imagines himself to be a dog (OED definitions).
The meaning of cynic in current usage is someone who does not believe in the sincerity or goodness of human motives, but Cynics were originally a school of philosophers in ancient Greece, whose aim was to live a life of virtue and who shunned fame, wealth and the comforts of life. The most famous among them was Diogenes, who begged for food and whatever he needed and lived in a barrel. He was often referred as Diogenes the Dog. He didn’t seem to mind this epithet and referred to himself as dog-like, in the sense that he had no shame, couldn’t care less what others thought of him, and was not concerned with his food or surroundings.
The reason why the school of philosophers was named after the dog may be because Antisthenes, a pupil of Socrates considered the founder of Cynic philosophy, taught in a gymnasium called Cynosarges, meaning white, or swift, dog. People related the name to dogs, and began calling the Cynic scholars dog-like.
Diogenes is credited with being one of the first users, if not the first, of the term cosmopolitan ie citizen of the world, which is how he described himself when asked where he was from. His name is also immortalised in the medical condition known as Diogenes’ syndrome (which I blogged on here), which is to do with excessive hoarding – something Diogenes most definitely did not do.