These are not synonyms. These terms have distinct meaning.

• Private means that information is for your eyes only, yours and people with whom you communicate. Nobody else can peek into them. No advertizers, no big-tech, nobody...
• Secure means all the communication is encrypted with modern encryption methods and algorithms.
• Safe means this is your system and access to the system is granted by yourself, no abuse from strangers, no hate speech and no trolling.