kanajlo

The register ladder, mildest first. Fripono is a rogue or a rascal: a cheat, a swindler, someone who will take your money, and the word carries a faint indulgence - a fripono can be likeable in a story. Bubo is a brat or an urchin: young, badly behaved, not yet dangerous. Kanajlo is the one with no warmth in it at all. The dictionary defines it as malnobla fripono - a base, ignoble version of the first word on this list - and that is exactly the right way to hold it. A fripono is a rogue. A kanajlo is a rogue with the charm taken out.

How writers use it. It is a literary insult rather than a street one: you will meet it in fairy tales and in nineteenth-century novels, aimed at the villain, and it is the standard Esperanto rendering of English blackguard and villain and Russian негодяй. As direct abuse it is strong. Kanajlo! shouted at somebody is a serious accusation about their character, not a complaint about their behaviour, and Esperanto speakers reach for it far less often than English speakers reach for bastard.

Derivations, and they are all in use. Kanajla is the adjective, kanajlaĵo a piece of villainy, kanajlaro the whole gang of them, kanajli to behave like one, and kanajlego an arch-villain. The collective is the oldest sense: French canaille meant a pack of dogs, from Latin canis, and it was applied to the mob long before it was applied to any individual. So the word began as an aristocrat's word for other people, which is worth knowing before you use it about anybody.