calculative (similar term)
conniving (similar term)
scheming (similar term)
shrewd (similar term)
case-hardened (similar term)
hardened (similar term)
hard-boiled (similar term)
steely (similar term)
difficult (related term)
hard (related term)
insensitive (related term)
merciless (related term)
unmerciful (related term)
tough (related term)
soft (antonym)