How do you say my father in Latin?

Depending on the grammatical context:

• meus pater (subject)
• mi pater ("O my father!")
• mei patris ("of my father")
• meo patri ("to/for my father")
• meum patrem (object of verb or some prepositions)
• meo patre ("by/with/from my father")

Latin Word order is flexible; any of these could have the Words in the opposite order.