Uncousinly is a rarely used word that describes behavior or actions that are lacking in cousinly kindness, warmth, or manners. Thankfully, there are several synonyms that can effectively capture the essence of this word. Discourteous, impolite, or ungracious perfectly describe the behavior that lacks the amiable qualities expected between cousins. Furthermore, uncivil or rude can be used interchangeably, highlighting the absence of consideration or respect associated with cousinly relations. Additionally, ill-mannered, tactless, or thoughtless efficiently convey the notion of behavior that falls short of the expected familial conduct. As such, these synonyms vividly paint a picture of actions that do not align with the qualities typically found between cousins.