Definition of "embouchure"

you could see the twin lines running down from either side of his lower lip, etched in by the force of his embouchure, looking like extensions of his mustache.

1963, Thomas Pynchon, V.

We approached Piteå at sunset. The view over the broad embouchure of the river, studded with islands, was quite picturesque, and the town itself, scattered along the shore and over the slopes of hills made a fair appearance.

1857, Bayard Taylor, “Northern Travel: Summer and Winter Pictures”, in Prose Writings of Bayard Taylor, revised edition, New York: G. P. Putnam, published 1862, page 180

Passing by Conical Rock, an isolated peak which forms a conspicuous landmark, the coast trends to the northward to Cape Dudley Digges and on to Cape Athol. Beyond Cape Athol lies Saunders Island, at the entrance to Wolstenholme Sound, which like most of these inlets, forms the embouchure of a glacier-river.

1885, Winfield Scott Schley, James Russell Soley, “The Gateway of the Polar Sea”, in The Rescue of Greely, New York: Charles Scribner’s Sons, page 6