Callous is a word used to describe someone who is unfeeling, unsympathetic, or indifferent. There are several synonyms for this word that can be used to convey a similar meaning. Words like unfeeling, insensitive, apathetic, indifferent, heartless, cold, and unemotional can be used in place of callous. Other synonyms include unsympathetic, unconcerned, uncaring, and unresponsive. Callous behavior is often considered harsh and cruel, and these words can help to emphasize that sentiment. Whether used in casual conversation or formal writing, these synonyms can help to effectively communicate the idea of someone who is lacking in emotional sensitivity.