Rare, poetic or literary term for 'butterfly'. The usual word is 蝶 (ちょう).
See also: 蝶
'Yumemidori' is one of the elegant terms for butterfly.
Compound of 夢 (yume, 'dream') + 見 (mi, 'seeing') + 鳥 (tori, 'bird'), literally 'dream-seeing bird'. The exact origin of this poetic name for butterfly is uncertain.