1.
grandfather
One's grandfather or someone else's grandfather.
2.
elderly man, old man
An older gentleman.
おじいさん refers to grandfather or elderly men in general.
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- おじいちゃん: grandpa (casual/affectionate)
- おじいさん: grandfather (polite)
- 祖父: grandfather (humble, formal)
- お祖父さん: the same word written with kanji
Usage
1. One's own grandfather or someone else's
2. An elderly man in general
When addressing strangers, おじいさん can be used for elderly men but may be considered slightly rude in formal contexts.
Similar words
Cultural note
昔話 (folktales) often begin with おじいさんとおばあさんがいました (There lived an old man and an old woman).
Related Words
Keigo:
祖父 (humble)
Related:
おばあさん (grandmother)
Compare:
おばさん (aunt / middle-aged woman)
Related:
おじ (uncle)
Compare:
おじいちゃん (grandfather)
Related:
祖父母 (grandparents)