These words pertain to harsh or harmful acts that inflict pain on others or to inhumane temperaments and attitudes that are lacking in sensitivity or compassion. Cruel can apply to both the act and the attitude: the cruel way he mistreated the helpless child; cruel and vicious prison warders. While the word can suggest the gratuitous or unmotivated infliction of pain, cruel is also used to describe situations where punishment may be deserved or thought desirable, but is meted out unjustly or excessively: a constitutional ban on cruel and unusual punishment; a cruel and repressive régime. But the word can also apply to anything that causes pain or harm, even where all intent to hurt or punish is absent: the cruel sea; the cruel , inexorable forces of nature. By contrast, sadistic always implies a deliberate wish to cause pain

and even more specifically focuses on inflicting it for its own sake rather than out of necessity or as punishment. The word suggests a warped mind that gets pleasure from seeing or causing other living things to suffer: the disturbed child who tore butterflies apart with sadistic gusto; a sadistic man who got sexual release only from flogging his female partner. Such pleasure often masquerades itself in the guise of meting out necessary discipline or authorized punishment.

Brutal and bestial both compare cruel behaviour to that of animals. Brutal emphasizes a lack of sensitivity or compassion and can suggest a gross and unintelligent person given to the use of excessive and indiscriminate force in attaining his objective: Many a movie mogul reached the top by trampling on others in the most brutal way. By contrast, it is possible to be both clever and cruel ; also, the sadistic mentality may contrive intricate ways of inflicting pain. Brutal alone stresses sheer, savage force. Because of this, brutal , like cruel , can be used to refer to non-human actions, especially those that are harsh or energetic. The ship was beleaguered by the brutal pounding of the violent storm. Bestial is applied exclusively to humans; it does not point solely to forcefulness as does brutal nor necessarily to the inflicting of pain like the first pair. It indicates, instead, any sort of behaviour that is thought unworthy of a human being because of its depravity, degeneracy or viciousness: the bestial society that gave rise to Auschwitz and Treblinka. In a related use, the word can apply to unrestrained or unnatural appetite of any sort: the bestial lust he felt for his own daughter. As Mark Twain pointed out, it may well be inaccurate to call cruel behaviour bestial , since most animals inflict pain only out of such necessities as hunger and self-defence, whereas man has often been known to do so gratuitously.

Nasty is the mildest of these words; at its most informal it can describe anything that is severe, serious or harmful: a nasty cut. Used of behaviour, it points to extreme unkindness or callousness and not necessarily to inflicting physical pain at all: She told him that she wouldn’t put up with his nasty remarks any longer. In describing personality, it can point to an extremely disagreeable temperament or to a habitual mistreatment of other: He woke up in a nasty frame of mind; a nasty man who treated other people like dirt.