おじいさん
おじいさん · ojiisan · JLPT N5 · noun
grandfather
👴 o (polite) + jii (grandpa) + san (Mr.) = honourable Mr. Grandpa
The core is jii (grandpa), wrapped in the polite prefix o- and the title -san. The long ii matters: ojisan with a short i means uncle. Longer vowel, older man — grandpa gets the extra i.