crossbill
鶍 refers specifically to the crossbill, a bird whose beak tips cross over each other. The meaning is a single concrete bird species.
鶍 is a Japanese kokuji (国字) created from 易 and 鳥. The exact reasoning behind the component choice is uncertain, but it likely combines the bird radical with a phonetic or semantic element specific to the crossbill.
The left side 易 suggests 'easy' or 'change', and the right side 鳥 is a bird. Picture a bird whose beak is easily changed—crossed at the tips like a crossbill's beak.
For いすか, imagine a crossbill sitting on a chair (椅子, いす) and calling 'ka!' (か). The chair (いす) plus 'ka' (か) gives いすか.
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