Neighbourly means behaving like a good neighbour: friendly, helpful, and ready to look after the people who live next to you. Taking in a parcel, watching someone's cat, or checking on the older person next door are neighbourly things. It is a warm, everyday word, a little old-fashioned in a kind way, and more at home in British English — Americans usually write neighborly. People also stretch it to countries: neighbourly relations means two countries that sit next to each other trying to get along and help, not fight. Though actually, it is about the spirit of being next-door, not only the house next door. You would not use it for a deep friendship; it is the lighter, decent kindness of people who share a street — or a border.