The word nice is a term commonly used in our language when we want to express about someone who is attentive and pleasant in his interaction and deal with the people with whom he relates. So when an individual behaves with sympathy, with good manners and a lot of cordiality we say it's kind.
Meanwhile, the kind word is closely related to the concept of amiability what comes to be state of behaving in a benevolent, pleasant and highly charitable manner towards those individuals with whom one interacts. Those who are naturally kind will always be willing to lend a hand to those who need it and if, for example, they see an elderly lady who is about to cross the street with difficulty, they will immediately stop doing what they are doing and will run to assist her at the crossing. .
It should be noted that kindness can always be present in the way of being a person and therefore, they will always lead and act guided by it, although, also, kindness can occasionally appear in the way of behaving of someone as a consequence of complying with what is socially accepted and expected of people as they live in community, and also someone may feign kindness with the mission of fulfilling or achieving a certain objective or end. In the latter case, kindness will not be a pure quality but will be imposed.
On the other hand, and due to its connection with courtesy, attention and service, the word friendly is used in our language as courtesy indicator at the time of requesting any question, request. So it is common that we find the following expression: "Could you be so kind as to serve me less milk than coffee, thank you".
The absolute opposite of kind is the rude, the rude, the unpleasant and the unfriendlyTherefore, when you want to express the opposite of friendly, it is usual for us to use any of these words.
