Paternal grandfather / grandmother

Literally

father's father / father's mother

When to use it

Dada is your father's father; Dadi is your father's mother. (Your mother's parents are nana/nani.) In Hindu families and in West Bengal, dada usually means an elder brother, so the meaning depends on who is speaking.

How it feels

Warm, respectful.

Formality

Familiar but respectful