1.
younger brother (polite — referring to someone else's)
Polite term for the listener's or a third party's younger brother. The honorific さん makes it appropriate for talking about others; one's own younger brother is 弟 (without さん).
Polite reference form for someone else's younger brother — 弟 + the honorific suffix さん. Do not use for one's own younger brother when speaking to outsiders.
Usage
- Used when talking about the listener's or a third party's younger brother
- For one's own younger brother (to outsiders): 弟
- Within the family, older siblings call a younger brother by name, not by 弟さん
Common collocations
- 弟さんはおいくつですか: How old is your younger brother?
- 弟さんによろしく: Say hi to your younger brother
- 弟さんとそっくり: looks just like your younger brother