"Thought to be a sign of the devils' offspring and clumsiness, ugliness and other sinister qualities, the medical (clinical) designation for being left-handed is 'SINISTRomanual'. Left-handedness is called 'SINISTRality' (that's right,...SINISTER without the 'E'). "
In Latin, the word for 'left' is 'sinister'. That is why those medical terms use that base. The attitude of left-handed people being the work of the devil led to the English word 'sinister'.