尾 means “tail, end”

お · o

Also: counter for fish, lower slope of mountain

Kun'yomi (Japanese reading)
お
On'yomi (Chinese reading)
ビ

JLPT N1 · Taught in secondary school · 7 strokes

The story

Fur (毛) trailing behind a body (尸): a tail. 尻尾 is an animal's tail, 尾行 is tailing a suspect, 語尾 is the tail end of a word, and a mountain's 尾根, its long ridge, trails off like a tail.

Used in 尻尾 (shippo, tail), 尾行 (bikou, tailing someone), and 尾根 (one, mountain ridge)

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Readings from KANJIDIC2, © EDRDG, CC BY-SA.