Kinslaying is a great taboo in Westeros. When a member of family kills a relation he/she is dubbed a kinslayer. Any individual who slays a member of their own family is believed to be cursed forever in the sight of gods and men.  Many Lords and smallfolk believe this and thus those who slay their own blood are usually looked down upon or shunned. There is a saying... (old gods or new gods)
No man is so accursed as the kinslayer.
People accused of kinslaying
- Stannis Baratheon – conceived a shadow assassin with Melisandre that went on to slay his brother King Renly Baratheon. His maester Cressen considers the thought of killing Renly:
Fratricide . . . my lord, this is evil, unthinkable . .
- Tyrion Lannister: accused of the murder of his nephew, King Joffrey I, of which he's actually innocent. Also held responsible for the murder of his own father, Tywin Lannister, of which he is actually guilty.
- Ramsay Bolton: his own father, Roose Bolton, suspects he poisoned his half-brother Domeric, Roose's trueborn son.
- Robb Stark: when preparing to execute Rickard Karstark, per Eddard Stark's custom that the man who passes the sentence should also swing the sword, Karstark calls Robb a kinslayer due to the (distant) blood ties between Starks and Karstarks.
- Theon Greyjoy: named a kinslayer by some for his supposed murder of Bran and Rickon Stark, as he was their father's ward, although they are not his blood kin.
Historical Kinslayers or suspected of Kinslaying
32pxJonos Arryn called Jonos the Kinslayer when he killed his own brother, Ronnel during the reign of King Aenys.
32pxKing Maegor I the Cruel: For slaying his nephew Aegon Targaryen and having his other nephew Viserys Targaryen tortured until he died.
King Aegon II: For feeding his half-sister Rhaenyra Targaryen to his dragon Sunfyre during the Dance of the Dragons.
32pxAemond Targaryen: For killing his nephew Lucerys Velaryon during the Dance of the Dragons.
32pxKing Viserys II: Was alleged to have poisoned his nephew Baelor the Blessed.
32pxKing Aegon IV the Unworthy: Was alleged to have poisoned his father Viserys II.
King Maekar I: Was called a kinslayer when he slew his own brother Baelor "Breakspear" Targaryen (although it was an accident).
Brynden Rivers: Was called a Kinslayer when he killed his half-brother Daemon Blackfyre during the Battle of the Redgrass Field.
32pxMaelys Blackfyre: Was called a kinslayer because he supposedly consumed his own twin in the womb.
Ser Erryk: For slaying his twin brother Ser Arryk during the Dance of the Dragons; each died by the other's sword.
Ser Arryk: For slaying his twin brother Ser Erryk during the Dance of the Dragons; each died by the other's sword.
32px Lord Stark (grandson of Brandon the Daughterless): Slew Bael the Bard, the King-Beyond-the-Wall, ignorant that he was his actual father.
- Customs for additional information on customs and traditions of Westeros.
- Jaime's thoughts
The gods hate kinslayers, even when they kill unknowing. 
Kinslaying is dry work. It gives a man a thirst. 
The gods hate kinslayers. 
References and Notes
- A Clash of Kings, Chapter 44, Tyrion X.
- A Feast for Crows, Chapter 18, The Iron Captain.
- A Feast for Crows, Chapter 29, The Reaver.
- A Clash of Kings, Prologue.
- A Storm of Swords, Chapter 70, Tyrion X.
- A Dance with Dragons, Chapter 27, Tyrion VII.
- A Dance with Dragons, Chapter 32, Reek III.
- A Storm of Swords, Chapter 20, Catelyn III.
- A Dance with Dragons, Chapter 46, A Ghost in Winterfell.
- The World of Ice & Fire, Viserys II.
- A Clash of Kings, Chapter 51, Jon VI.
- A Storm of Swords, Chapter 62, Jaime VII.
- A Clash of Kings, Chapter 51, Jon VI, p 545.
- A Dance with Dragons, Chapter 1, Tyrion I.
- A Dance with Dragons, Chapter 56, The Iron Suitor.