IPA: //koʊldˈhɑːrtɪdnəs//
KK: /koʊldˈhɑːrtɪdnəs/
The quality of being emotionally unfeeling or lacking compassion towards others.
His coldheartedness made it difficult for him to connect with his friends.
Coldheartedness → It is formed from "cold" (from Old English "cald", meaning lacking warmth) and "heartedness" (from "heart" which comes from Old English "heorte", meaning the organ of emotion or feeling, combined with the suffix "-ness" meaning the state or quality of). The word describes the state of having a heart that is devoid of warmth or compassion.
Think of someone who is 'lacking warmth' ('cold') in their 'emotions' ('heartedness') — that's why coldheartedness means being emotionally unfeeling.