bird of (one's) own brain(redirected from bird of their own brain)
bird of (one's) own brain
obsolete A thought or idea of one's own conception, especially that which is confidential or unknown to others. I know not what she thinks of me, for that is a bird in her own brain and kept from my eyes.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.