Webster's Revised Unabridged Dictionary · 1913

Blue bonnet

Blue bonnet ({not transcribed}) , noun

1.
A broad, flat Scottish cap of blue woolen, or one wearing such cap; a Scotchman.
2.
(Botany) A plant. Same as Bluebottle.
3.
(Zoology) The European blue titmouse (Parus coruleus); the bluecap.

Also: Blue-bonnet