noun
younger brother (of an older brother); younger sister (of an older sister)
Archaic term for a younger sibling from the perspective of an older sibling of the same sex. In modern Japanese, 弟 (おとうと) is used for younger brother and 妹 (いもうと) for younger sister.
古語では、兄から見た弟を「おと」と呼んだ。
In classical Japanese, an older brother called his younger brother 'oto'.
noun
Archaic noun for the youngest child in a family. This usage is obsolete; modern Japanese uses 末っ子 (すえっこ) or 末子 (まっし).
「おと」は末の子を指す古い言い方で、今はほとんど使われない。
'Oto' is an old word for the youngest child and is hardly used today.
prefix
young; younger; youngest; young and beautiful; cute
Archaic prefix indicating youth or junior status, sometimes with a nuance of beauty or cuteness. Found only in old compounds; not productive in modern Japanese.
「弟橘姫」の「弟」は「おと」と読み、若い女性を表す接頭語である。
The '弟' in 'Ototachibana-hime' is read 'oto' and is a prefix meaning young woman.
Modern standard word for 'younger brother', replacing the archaic おと.
Modern standard word for 'younger sister', replacing the archaic おと when used for a younger sister of an older sister.
Common modern word for 'youngest child', replacing the archaic おと in that sense.
The historical derivation is uncertain. The kanji 弟 and 乙 are conventionally associated with the meanings 'younger sibling' and 'youth', but the word おと itself is archaic and its origin is not clearly documented.