To manually input a nickname, open any contact card, tap Edit, choose Add field, and select Nickname from the list. Siri will also remember your relationships. Tell the assistant to “call mom” or “call my boss,” and it’ll ask which contact that designation belongs to and whether it should remember for future calls. If you want to manually assign a relationship, tap on your own contact card, hit Edit, and then add related name. Choose from a number of different relationships and tap the "i" icon to link that relationship to a specific contact.