partridge
鴣 refers specifically to a partridge, a type of bird.
鴣 is a phono-semantic compound: the left component 古 (old) likely provides the sound コ, while the right component 鳥 (bird) indicates the meaning. The exact historical development is uncertain.
An old (古) bird (鳥) that is a partridge.
For コ, imagine an old partridge cooing softly: coo -> コ.
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