Is it permissible to use the nickname "Mino" for my nephew whose name is Muhammad, knowing that "Mino" is a nickname for the Christian name "Mina", and does this constitute imitation of non-believers? And is it permissible to use nicknames for boys in general?

Fondling and caressing a child by using a diminutive of their name or calling them by another name out of endearment is permissible. Indeed, the Prophet, peace and blessings be upon him, called Al-Hasan (definition) "Luqaʿ". "Luqaʿ" refers to a small child who does not respond to logic or whose speech is unclear. However, a child should not be called by a name exclusive to Christians, as this constitutes imitation of them. The matter becomes even more reprehensible if it replaces a noble name like "Muhammad".