Final answer:
The word 'steadfast' means unwavering and firm. In the context, 'white Mississippi' is described as having a steadfast belief, which is firm and does not waver.
Step-by-step explanation:
The word 'steadfast' means unwavering and firm. In the context provided, the author describes 'white Mississippi' as having a steadfast belief. This implies that their belief is firm and does not waver. The excerpt mentions that to doubt was considered rank infidelity, indicating that their belief was strong and unwavering despite the difficult circumstances of the Confederacy.