'Bird's-mouth' definitions:

Definition of 'Bird's-mouth'

From: GCIDE

Bird's-mouth \Bird's-mouth`\, n. (Arch.) An interior angle or notch cut across a piece of timber, for the reception of the edge of another, as that in a rafter to be laid on a plate; -- commonly called crow's-foot in the United States. [1913 Webster] Bird's nest