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1.
emotionally hardened; cold-blooded and indurate to public opinion;
I have become so callous towards your constant critizizam
by Eloise. December 07, 2008
 
2.
Not giving a rat's ass about anything.
The extreme of all apathy.
Not giving a fuck.
Lack of all things binding one's emotions to any actions they commit.
That man is so callous. He has a family of a wife and six kids but he still drove his car off of a cliff and into a pile of burning tires because his friend said, "Do it, you won't."
by Clinik December 23, 2009
 
3.
Uncaring, indifferent or unconcerned about the feelings or needs of others, heartless, cruel.
The wealthy industrialist rolled his eyes in callous disdain as he brushed past a crying child begging for help.

The school bully callously humiliated a helpless newcomer.
by Lorelili November 18, 2012
 
4.
thick-skinned english teacher
BFFADS is an extremely callous man.
He is so callous man.
by JasonPenney May 20, 2007